CVE-2026-59999 — openssh-portable
MEDIUMCVE-2026-59999 is a medium-severity (CVSS 5.9) CWE-348 vulnerability. A fix is available — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-59999.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-59999 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Description
In sshd in OpenSSH before 10.4, DisableForwarding=yes was supposed to take precedence over PermitTunnel=yes, but did not.
Affected Products
opensshopenbsdDetection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Fix
Upgrade the affected component to the fixed release for CVE-2026-59999, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This Moderate severity flaw in OpenSSH `sshd` allows `PermitTunnel=yes` to override `DisableForwarding=yes`, potentially bypassing intended security controls. In Red Hat environments where `DisableForwarding` is used to restrict SSH session capabilities, an attacker who compromises a user's session could still…
To mitigate this issue, if `DisableForwarding=yes` is set in `/etc/ssh/sshd_config` to prevent all forwarding, ensure that `PermitTunnel` is explicitly set to `no` in the same configuration file. This will enforce the intended security policy. After modifying `/etc/ssh/sshd_config`, restart the `sshd` service for the changes to take effect. This may temporarily interrupt active SSH sessions.Source: Red Hat security advisory for CVE-2026-59999 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | openssh-0:9.9p1-27.el10_2 | RHSA-2026:69129 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | openssh-0:9.9p1-7.el10_0.5 | RHSA-2026:76748 |
| Red Hat Enterprise Linux 8 | openssh-0:8.0p1-33.el8_10 | RHSA-2026:69266 |
| Red Hat Enterprise Linux 9 | openssh-0:9.9p1-11.el9_8 | RHSA-2026:69130 |
| Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions | openssh-0:8.7p1-38.el9_4.10 | RHSA-2026:76993 |
| Red Hat Hardened Images | openssh-main-10.4p1-1.hum1 | RHSA-2026:37382 |
| Red Hat Update Infrastructure 5 | rhui5/installer-rhel9:1790241922 | RHSA-2026:71603 |
Frequently Asked Questions
Is CVE-2026-59999 in your dependencies?
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