CVE-2026-39832

When a key was added to a remote SSH agent with constraint extensions, the library did not include these extensions in the serialized request. This resulted in constraint extensions being silently stripped during key forwarding operations. The remote agent treated the forwarded key as unrestricted, ignoring the client's access control intentions. The vulnerability stems from improper handling of deserialization and serialization of constraint extensions (CWE-502).

An attacker or unauthorized process with access to a remote SSH agent can use the forwarded key without any restrictions on the destination, violating access control policies and enabling unauthorized authentication and potential modification of resources on remote hosts.

Patches available from the vendor should be applied according to references (https://go.dev/cl/778642, https://pkg.go.dev/vuln/GO-2026-5006). After updating, the library correctly serializes all constraint extensions, and the in-memory keyring returned by NewKeyring() rejects keys with unsupported extensions instead of silently ignoring them.

Golang Crypto library (golang.org/x/crypto) — versions indicated in vendor references; affects applications using key forwarding to remote SSH agents and the NewKeyring() function.