Week in review: Apache Struts vulnerability exploit attempt, EOL Sophos firewalls get hotfix

Apache Log4j2, an extremely widely used Java logging library, fails to protect its JNDI lookup feature against attacker-controlled JNDI-related endpoints (CWE-20, CWE-502), so crafted text processed by the logger causes the Java runtime to fetch and load attacker-supplied objects, leading to remote code execution. The flaw is triggered whenever attacker-controlled input reaches the logging API and is parsed for JNDI lookups, a pattern common in web servers and enterprise Java applications that log user-supplied fields such as headers or form values. Successful exploitation yields arbitrary code execution under the privileges of the affected application, giving attackers a foothold for lateral movement, data theft, and ransomware deployment. Any Java application or product that ships or bundles an affected Apache Log4j2 release is exposed, making this one of the most broadly deployed vulnerabilities ever disclosed. Exploitation is confirmed in the wild: CISA added it to the Known Exploited Vulnerabilities catalog on 2021-12-10 with known ransomware use, and EPSS assigns a 100% probability of exploitation within 30 days.

Do: Inventory all Java applications and dependencies for Apache Log4j2 and apply the vendor's patched updates, or remove affected assets from the network, as required by CISA's KEV catalog. Where updates are not yet available, use the temporary mitigations in CISA's ED-22-02 recommended-mitigation guidance, such as disabling message lookups, only until patches are applied. Prioritize internet-facing and business-critical systems and hunt for exploitation activity given known ransomware use.

CVE-2022-3236 is a critical (CVSS 9.8) code injection flaw (CWE-94) in the User Portal and Webadmin interfaces of Sophos Firewall version v19.0 MR1 and older. A remote, unauthenticated attacker can send crafted input to an exposed User Portal or Webadmin service, and the network-reachable, no-privilege, no-user-interaction nature of the flaw makes it trivially triggerable once those interfaces are reachable. Successful exploitation results in arbitrary code execution on the firewall appliance, with high impact to confidentiality, integrity, and availability. Any organization running Sophos Firewall v19.0 MR1 or older is affected, including end-of-life appliances for which the vendor issued a dedicated hotfix. The flaw is confirmed exploited in the wild: it was abused as a zero-day before the patch, added to CISA KEV on 2022-09-23, carries a 98.9% EPSS, and news reports indicate it was still being exploited against EOL firewalls well after disclosure.

Do: Upgrade Sophos Firewall to version 19.5 or later per vendor instructions (the fix shipped in the 19.5 release line), and apply the vendor hotfix to end-of-life appliances that cannot upgrade. Restrict internet exposure of the User Portal (TCP 443) and Webadmin (TCP 4444) to trusted management IPs via WAN access rules, and review appliance logs for signs of exploitation. As this CVE is in CISA KEV, federal agencies and other defenders with KEV-driven patch mandates should confirm the update is applied.

JetBrains TeamCity Server, a widely used CI/CD build server, contains an authentication bypass vulnerability (CWE-288) that lets a remote, unauthenticated attacker gain administrative access without valid credentials. By sending crafted requests to the TeamCity server over the network, the attacker bypasses authentication and can then execute arbitrary code on the server via administrative and build features, achieving full remote code execution. An attacker gains control of the build server and, with it, access to source code, build artifacts, stored secrets and credentials, and a foothold for lateral movement or ransomware deployment. Any organization running an affected TeamCity Server is affected, especially instances reachable from the internet. Exploitation is confirmed in the wild: CISA added the flaw to its KEV catalog on 2023-10-04 with known ransomware use, and EPSS assigns a 100% probability of exploitation within 30 days.

Do: Upgrade TeamCity Server to 2023.05.4 or later per JetBrains' instructions, or apply vendor mitigations or discontinue use if patching is not possible (per the CISA KEV required action). Also take unpatched instances off the public internet, and hunt for signs of compromise such as unauthorized administrator accounts, unexpected changes in audit logs and build configurations, and stored secrets or tokens that may have been stolen, given known ransomware exploitation.

An attacker can manipulate file upload params to enable paths traversal and under some circumstances this can lead to uploading a malicious file which can be used to perform Remote Code Execution. Users are recommended to upgrade to versions Struts 2.5.33 or Struts 6.3.0.2 or greater to fix this issue.