OpenSSL: NULL dereference in SSL_check_chain crashes TLS 1.3 peers

CVSS 7.5CVE-2020-1967Kernel, userspace & hypervisorcurated

Impact

Any peer in a TLS 1.3 handshake can send an unrecognised signature algorithm in the signature_algorithms_cert extension and crash an application that calls SSL_check_chain() during or after the handshake. The affected process dies outright, so for a server-side service this is a remote unauthenticated crash loop and for a client it is a hang-free but fatal abort. On a GPU fleet the practical exposure is whichever TLS endpoints and node-local daemons are built against OpenSSL 1.1.1d-1.1.1f and use that callback path - a narrow set, since only applications calling SSL_check_chain are affected. No data is exposed; the vector is availability-only. Versions before 1.1.1d are not affected.

Who can reach it

Any TLS 1.3 peer that the vulnerable application talks to - a remote client against an exposed listener, or a malicious server against an outbound connection. No authentication required.

What to do

Update to OpenSSL 1.1.1g or the equivalent distribution package (openSUSE, Debian, FreeBSD 12.1 all shipped updates). Restart every service that has the shared library mapped; nothing here needs firmware work or a node drain, but a process restart is mandatory for the fix to take effect.

References

https://nvd.nist.gov/vuln/detail/CVE-2020-1967 http://www.openwall.com/lists/oss-security/2020/04/22/2 http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00004.html http://seclists.org/fulldisclosure/2020/May/5

This entry is curated: imported from vendor advisories with machine assistance, not yet individually verified. Confirm against your vendor's advisory before acting, and report anything wrong.