CVE-2026-39828
MediumCVSS 6.3Exploitation Probability (EPSS)
Low risk30th percentile - higher than 30% of all known CVEs
Summary
In SSH, when an authentication callback returned PartialSuccessError with non-nil Permissions, those permissions were silently discarded. This could drop certificate restrictions like force-command after a second factor. Returning non-nil Permissions with PartialSuccessError now results in a connection error.
Risk Assessment
An attacker can bypass SSH certificate restrictions, such as forced commands, after successful multi-factor authentication.
Recommendation
Update the SSH implementation to a version where PartialSuccessError with non-nil Permissions causes a connection error.
Other vulnerabilities in SSH
See all- CVE-2026-56854High
The source-address critical option in the Permissions returned by an authentication callback was only enforced for the PublicKeyCallback and VerifiedPublicKeyCallback paths, extending the fix for CVE-2026-46595. Permissions returned by the PasswordCallback, KeyboardInteractiveCallback, NoClientAuthCallback, and GSSAPIWithMICConfig.AllowLogin callbacks were not validated against the client's remote address, so a source-address restriction set by those callbacks was silently ignored. The check is now applied to the Permissions returned by any authentication callback.
- CVE-2000-0217Medium
The default configuration of SSH allows X forwarding, which could allow a remote attacker to control a client's X sessions via a malicious xauth program.
- CVE-1999-1231Medium
ssh version 2.0.12, and possibly other versions, allows valid usernames to attempt to enter the correct password multiple times, but only prompts for a password once for an invalid username. This allows remote attackers to determine user account names on the server.
- CVE-1999-1159Medium
SSH version 2.0.11 and earlier allows local users to request remote forwarding from privileged ports without being root.
Original NVD description (English source)
When an SSH server authentication callback returned PartialSuccessError with non-nil Permissions, those permissions were silently discarded, potentially dropping certificate restrictions such as force-command after a second factor succeeded. Returning non-nil Permissions with PartialSuccessError now results in a connection error.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS