Executive brief
A vulnerability in the Go SSH agent library allows security restrictions on digital keys to be bypassed when they are forwarded to remote servers. This means that a key intended to be used only for specific destinations or under certain conditions could be used without any restrictions by a remote host. This could lead to unauthorized access to other systems if a remote server is compromised or untrustworthy.
Technical details
A vulnerability exists in the golang.org/x/crypto/ssh/agent package where constraint extensions, such as 'restrict-destination-v00@openssh.com', are not serialized during the key-adding process to a remote agent. This results in the silent stripping of these security constraints, allowing a forwarded key to be used without the intended restrictions on the remote host. The root cause is a failure in the serialization logic within the client.Add and keyring.Add functions. Attackers can exploit this to use keys in ways explicitly forbidden by the original security policy. The issue is fixed in version 0.52.0, which properly serializes all constraint extensions and ensures the in-memory keyring rejects keys with unsupported extensions.
Affected products
- Go Project golang.org/x/crypto/ssh/agent < 0.52.0
Timeline
- 2026-05-16: disclosed: Issue reported to Go project
- 2026-05-22: advisory: NVD and Go vulnerability report published
- 2026-06-25: advisory: GitHub Advisory published