CVE-2023-38408

The PKCS#11 feature in ssh-agent in OpenSSH before 9.3p2 has an insufficiently trustworthy search path, leading to remote code execution if an agent is forwarded to an attacker-controlled system. (Code in /usr/lib is not necessarily safe for loading into ssh-agent.) NOTE: this issue exists because of an incomplete fix for CVE-2016-10009.

Weakness

The product uses a search path that contains an unquoted element, in which the element contains whitespace or other separators. This can cause the product to access resources in a parent path.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

References

• http://packetstormsecurity.com/files/173661/OpenSSH-Forwarded-SSH-Agent-Remote-Code-Execution.html
• http://www.openwall.com/lists/oss-security/2023/07/20/1
• http://www.openwall.com/lists/oss-security/2023/07/20/2
• http://www.openwall.com/lists/oss-security/2023/09/22/11
• http://www.openwall.com/lists/oss-security/2023/09/22/9
• https://blog.qualys.com/vulnerabilities-threat-research/2023/07/19/cve-2023-38408-remote-code-execution-in-opensshs-forwarded-ssh-agent
• https://github.com/openbsd/src/commit/7bc29a9d5cd697290aa056e94ecee6253d3425f8
• https://github.com/openbsd/src/commit/f03a4faa55c4ce0818324701dadbf91988d7351d
• https://github.com/openbsd/src/commit/f8f5a6b003981bb824329dc987d101977beda7ca
• https://lists.debian.org/debian-lts-announce/2023/08/msg00021.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CEBTJJINE2I3FHAUKKNQWMFGYMLSMWKQ/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RAXVQS6ZYTULFAK3TEJHRLKZALJS3AOU/
• https://news.ycombinator.com/item?id=36790196
• https://security.gentoo.org/glsa/202307-01
• https://security.netapp.com/advisory/ntap-20230803-0010/
• https://support.apple.com/kb/HT213940
• https://www.openssh.com/security.html
• https://www.openssh.com/txt/release-9.3p2
• https://www.qualys.com/2023/07/19/cve-2023-38408/rce-openssh-forwarded-ssh-agent.txt
• https://www.vicarius.io/vsociety/posts/exploring-opensshs-agent-forwarding-rce-cve-2023-38408