threat-analysis
Active Exploitation of Unpatched Citrix Devices
On 18 July 2023, Citrix issued an advisory stating that a Remote Code Execution (RCE) vulnerability in older installations of NettScaler ADC was being actively exploited in the wild. The RCE vulnerability was assigned CVE-2023-3519 with a CVSS severity score of 9.8. There were 2 additional CVEs disclosed in the advisory CVE-2023-3466 and CVE-2023-3467.
The products affected by the vulnerabilities are as follows:
- NetScaler ADC and NetScaler Gateway 13.1 before 13.1-49.13
- NetScaler ADC and NetScaler Gateway 13.0 before 13.0-91.13
- NetScaler ADC and NetScaler Gateway version 12.1 (EOL)
- NetScaler ADC 13.1-FIPS before 13.1-37.159
- NetScaler ADC 12.1-FIPS before 12.1-55.297
- NetScaler ADC 12.1-NDcPP before 12.1-55.297
The Cybersecurity and Infrastructure Security Agency (CISA) disclosed that CVE-2023-3519 was used in an attack against critical infrastructure. The attacker leveraged the RCE vulnerability to drop a web shell to enumerate and exfiltrate Active Directory data.
Analysis: Threat actors have increased targeting of Software-as-a-Service providers as a method of gathering more victims and as an adjustment to organizations moving to more cloud-based solutions. Recent compromises like MoveIT by Cl0p and Fortinet FortiOS by Chinese threat actors will be more common vectors of approach by threat actors.
Actions: Citrix has released a patch for the vulnerabilities, but for organizations that are unable to patch or require further guidance, detection methods and Indicators of Compromise will be available in the TECHNICAL DETAILS portion of this report.
TECHNICAL DETAILS
Detection methods
- Check for newer files than the last installation
- Modify the -newermt parameter with date that corresponds to your last installation
- find /var/vpn/ -type f -newermt [YYYYMMDD] -exec ls -l {} \;
- find /var/netscaler/logon/ -type f -newermt [YYYYMMDD] -exec ls -l {} \;
- find /var/python/ -type f -newermt [YYYYMMDD] -exec ls -l {} \;
- Check http error logs for abnormalities that may be from initial exploit:
- zgrep ‘\.sh’ /var/log/httperror.log*
- zgrep ‘\.php’ /var/log/httperror.log*
- Check shell logs for unusual post-ex commands, for example:
- grep ‘/flash/nsconfig/keys’ /var/log/sh.log*
- Look for setuid binaries dropped:
- find /var -perm -4000 -user root -not -path “/var/nslog/*” -newermt [YYYYMMDD] -exec ls -l {} \;
- Review network and firewall logs for subnet-wide scanning of HTTP/HTTPS/SMB (80/443/445) originating from the ADC.
- Review DNS logs for unexpected spike in internal network computer name lookup originating from the ADC (this may indicate the threat actor resolving host post-AD enumeration of computer objects).
- Review network/firewall logs for unexpected spikes in AD/LDAP/LDAPS traffic originating from the ADC (this may indicate AD/LDAP enumeration).
- Review number of connections/sessions from NetScaler ADC per IP address for excessive connection attempts from a single IP (this may indicate the threat actor interacting with the webshell).
- Pay attention to larger outbound transfers from the ADC over a short period of session time as it can be indicative of data exfiltration.
- Review AD logs for logon activities originating from the ADC IP with the account configured for AD connection.
- If logon restriction is configured for the AD account, check event 4625 where the failure reason is “User not allowed to logon at this computer.”
- Review NetScaler ADC internal logs (sh.log*, bash.log*) for traces of potential malicious activity (some example keywords for grep are provided below):
- database.php
- ns_gui/vpn
- /flash/nsconfig/keys/updated
- LDAPTLS_REQCERT
- Ldapsearch
- openssl + salt
- Review NetScaler ADC internal access logs (httpaccess-vpn.log*) for 200 successful access of unknown web resources.
IOCs
| 14.1.1.0 | IP Address |
| 12.2.1.4 | IP Address |
| 6.4.0.0 | IP Address |
| 3.0.0.4 | IP Address |
| 8.1.0.0 | IP Address |
| 21.0.7.4 | IP Address |
| 2.0.2.2 | IP Address |
| 21.4.3.0 | IP Address |
| 3.5.0.1 | IP Address |
| 1.44.7.1 | IP Address |
| 9.2.7.4 | IP Address |
| 1.45.4.1 | IP Address |
| 3.1.1.3 | IP Address |
| 1.7.42.2 | IP Address |
| 11.1.2.3 | IP Address |
| 7.0.0.0 | IP Address |
| 21.0.7.6 | IP Address |
| 9.1.0.4 | IP Address |
| 1.46.6.1 | IP Address |
| 1.43.7.2 | IP Address |
| 3.5.6.9 | IP Address |
| 7.6.0.3 | IP Address |
| 3.2.0.0 | IP Address |
| 11.2.13.0 | IP Address |
| 8.1.4.0 | IP Address |
| 3.1.0.2 | IP Address |
| 1.7.8.2 | IP Address |
| 8.1.17.0 | IP Address |
| ec78daac7c3d97966f2e3703ca5d1685 | MD5 |
| 9789d70454a47764b611afc8e84d6c0d | MD5 |
| a4eda2813d85d8b414bb87e855ab4bf8 | MD5 |
| 9fe61cf2edee63152161ffc52c39f6cd | MD5 |
| c96d775881f0476b9ef465dba9c6d9b8 | MD5 |
| 6c05518b807d014ee8edb811041e3de232520c28 | SHA-1 |
| 71bbed12f950de8335006d7f91112263d8504f1b | SHA-1 |
| 98a0688036e9dbcf43fa84960d9a1ef3e09a69cf | SHA-1 |
| 043e3c7dd683113e2b1c15cacb9c8e68f76513ff | SHA-1 |
| 46f4ebbe842620f0976a36741a72482620aa4b48 | SHA-1 |
| f4b1c488206e1b1581b06fcd331686846f13f19c | SHA-1 |
| 28282bc644054e157c3b9a3d38f1f9551ce09074 | SHA-1 |
| 52b003d915761f1581ae2d105f3cbe76df7bf1ff | SHA-1 |
| 8173f6512ab6183fa5edc5c9a5f3760b8979271e | SHA-1 |
| 00e2f5eea29994d19293ec4e8c8775ba73678598 | SHA-1 |
| 6cbea7d29b5285692843bc1c351abba1a7ef326f | SHA-1 |
| 9708fda28ccd0466cb0a8fd409854ab4d92f7dca | SHA-1 |
| 6323b355bd7f5d2ce85d0244fe0883af3881df4e | SHA-1 |
| d9c88ddc4c0c78fa534bd33237e95dea66003d29 | SHA-1 |
| 7325e9a5e71e2fc0e350487ecac7d84acdf0ed5e | SHA-1 |
| 6a83f0c958811f07e0d11dfc6b5a6a98edfd5bdc | SHA-1 |
| 02f76c401d17e409ed45bf7887148fcc22c93c85 | SHA-1 |
| 8a2dc82148844767f7c7728633a03dcee812e56a | SHA-1 |
| e9c1e65d58b47aec8cd676bd5c07d97b002f205e | SHA-1 |
| 7cd8d016edc74a78af0d81c948bfafbcc93c937c | SHA-1 |
| b4a402f41cf44b6094b5131286830ba9bb1eb290 | SHA-1 |
| 4bedf9eee016286c835e3d8fa981ddece5338795 | SHA-1 |
| 0237527b3244d251fa5ecd4912dfe4f8b2125c54 | SHA-1 |
| d64a487407d6f9685d3907206954a6c84c6fa621 | SHA-1 |
| e641968979d4a2377bbea5e2a76bdede040d0b97 | SHA-1 |
| 5aea738463960d81821c11ae7ade1d627a46bf32 | SHA-1 |
| 85fa76d77ed69927d24decf476e69bedc7691f48 | SHA-1 |
| 8beaace082b325e693dc7682029a3cb7e6c2b69d | SHA-1 |
| 391dd7f0f239020c46bf057cfa25f82031fc15f7 | SHA-1 |
| 7bc29a9d5cd697290aa056e94ecee6253d3425f8 | SHA-1 |
| d75888a9b14baaad591548463cca09dfd1395236 | SHA-1 |
| 2b9b8f3b68edb3d67d79962f02e26dbb5ae3808d | SHA-1 |
| 443d61d1fa9faa60ef925513d83742902390100f | SHA-1 |
| 0f03b3e5b7c1409998a13aba3a95396e6fa349d8 | SHA-1 |
| 9337fb3f2ab2b5f38d7e98a194bde6f7e3d16c40 | SHA-1 |
| 368ba06881c395f1c9a7ba22203cf8d78b4addc0 | SHA-1 |
| 6ecaab1d375f33165fe98d06d92f36c949c0ea11 | SHA-1 |
| 7c18543d126e8a567b83bb4535631825aaa9d742 | SHA-1 |
| 04c55383fa5689357bcdd2c8036725a55ed632bc | SHA-1 |
| dcaad2540f7d50c512ff2e031d3778dd9337db2b | SHA-1 |
| 0ef151550d96cc4460f98832df84b4a1e87c65e9 | SHA-1 |
| 8780a896543a654e757db1b9396383f9d8095528 | SHA-1 |
| 3e337087c3b5805fe0b8a46ba622a962880b5d64 | SHA-1 |
| 6dde93758d42455cb90ef324407919ed67668b9b | SHA-1 |
| ca54623333875b9beaad92c999a92b015c44b079 | SHA-1 |
| 019114cb788d954c5d1b36d6c62418619e93a757 | SHA-1 |
| 83ca1abb11ffe34211db55dcd36d96b94252827a | SHA-1 |
| 0662b99dfdec1ce07439eb7bed02d90320acc721 | SHA-1 |
| dd59cbac5f86057d6a73b87007c08b8bfa0c32ac | SHA-1 |
| a4b154bdf35b3465320136fcb078f196b437c2f1 | SHA-1 |
| b4c62101a43051fc7f5349c7d0a5b6085375c1d7 | SHA-1 |
| 9a0a4d3c1e7138915563c0df4fe6a3f9377b839c | SHA-1 |
| e17b80cff4975ee343568ff526b62319f499005d | SHA-1 |
| c67bbd8756f015e33e4ba639a40c7f9d8bd9e8ab | SHA-1 |
| fffb0b52d5258554c645c966c6cbef7de50b851d | SHA-1 |
| 95ce3d86bd2c53009108ffda2dcf553312d733db | SHA-1 |
| fc9867c1e03c22ebf56943be205202e576aabf23 | SHA-1 |
| 705bf1facbffd2ca40b159b0303132b6fdf657ad | SHA-1 |
| 22fcd34c606f32129ebc967fc21f24fb708a98b8 | SHA-1 |
| 305ce4ff789261df7e3f6e72363d0703e025f80d | SHA-1 |
| 94e1c001761373b7d9450768aa15d04c25547a35 | SHA-1 |
| 1c1bcf2d3ea061613119b534f57507c377df20f9 | SHA-1 |
| f0a96d1aafd8964e1f9955c830a3e5cb3c60a90f | SHA-1 |
| b37b46019553089db4f22eb2fe998bca84b2cb64 | SHA-1 |
| 7fd2219f194a9ef2a8901bb131c5fa12272305ce | SHA-1 |
| 92811f07d39e4ad95c92003868f5f7309489d79c | SHA-1 |
| f03a4faa55c4ce0818324701dadbf91988d7351d | SHA-1 |
| 2ee636d318653fb1ab193803dafbfe3e371d4130 | SHA-1 |
| 529cf49103e0fdf4eeb970fa1f62fa508ebe7c3c | SHA-1 |
| f8f5a6b003981bb824329dc987d101977beda7ca | SHA-1 |
| d66585d14b1160712a8a9bfaf9769dd3da0e9a83 | SHA-1 |
| 1fa20cf2f506113c761777127a38bce5068740eb | SHA-1 |
| 0323bce598eea038714f941ce2b22541c46d488f | SHA-1 |
| f1a411873c85b642f13b01f21b534c2bab81fc1b | SHA-1 |