Database/Kernel, userspace & hypervisor
libssh2: pre-auth integer underflow crashes any client that negotiates AES-GCM
Impact
A server that negotiates an AES-GCM cipher during the handshake triggers an underflow in the blocksize minus aadlen minus tag-length computation, producing an out-of-bounds read and a memcpy with a near-SIZE_MAX length. The client process dies before authentication, so no credentials are needed on the attacker's side. The operational effect is availability of fleet automation rather than node compromise: SFTP-based dataset pulls, backup runs and config-management passes abort every time they touch the hostile endpoint, and a crash loop in a long-running agent can leave a node unmanaged. Distinct from CVE-2026-66032 in both code path and fix commit. Fixed in commit a2ed82d; through 1.11.1 is affected.
Who can reach it
A malicious or compromised SSH server reachable by a libssh2 client on your fleet. Crash occurs pre-authentication, during cipher negotiation.
What to do
Update libssh2 to a build containing commit a2ed82d40964bbc0d64cd717aa0a5a892117d2e6 (the record names no release version), then restart the daemons and agents that link it; rebuild anything statically linked. Node drains and reboots are not needed. As an interim measure, limit which SSH endpoints fleet tooling may dial.
References
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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.