CVE-2026-59849 Red Hat CVE debrief

Who should care

Defenders responsible for systems using libssh for authentication, especially those with certificate-based public key authentication configured, should assess exposure and prioritize updates. Red Hat Enterprise Linux users should review their systems for affected versions and apply advisories as necessary.

Why it matters

CVE-2026-59849 is a libssh flaw causing denial of service. Defenders should verify and update libssh, review authentication configurations, and apply Red Hat advisories as necessary.

• Potential denial-of-service attacks against libssh clients
• Need to verify and update libssh to the latest version
• Review and configure certificate-based public key authentication properly

Technical summary

The libssh library has a flaw in its automatic certificate-based public key authentication logic. This flaw can cause libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected by a server, resulting in a denial-of-service condition. The vulnerability has been assigned a CVSS score of 3.1 and affects various versions of Red Hat Enterprise Linux. Affected product deployments should be reviewed for exposure, especially those with certificate-based public key authentication configured. Defenders should prioritize verifying and updating libssh to mitigate potential denial-of-service attacks.

Defensive priority

Defenders should prioritize verifying and updating libssh to mitigate potential denial-of-service attacks. Systems using libssh for authentication should be reviewed for exposure, especially those with certificate-based public key authentication configured.

Recommended defensive actions

• Verify and update libssh to the latest version
• Review systems using libssh for authentication and certificate-based public key authentication
• Apply Red Hat advisories (RHSA-2026:42922, RHSA-2026:55855) as applicable
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD detail page provide information on the vulnerability. Red Hat has issued advisories (RHSA-2026:42922, RHSA-2026:55855) and a security page for CVE-2026-59849. Bugzilla entry 2498182 tracks the issue.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.