The vulnerability CVE-2026-55655 in OpenSSH allows a local unprivileged attacker on a Linux client host to hijack client-side X11 forwarding connections by pre-binding the preferred abstract X socket name when X11 forwarding is enabled and a local UNIX-domain X socket is used. This flaw can compromise the confidentiality of forwarded X11 traffic, including sensitive window contents and input, and may allow some manipulation of the forwarded session. Red Hat has released security updates for OpenSSH in Red Hat Hardened Images and Red Hat Enterprise Linux 8 to fix this issue.

Successful exploitation allows a local unprivileged attacker to compromise the confidentiality of X11 forwarded traffic, potentially exposing sensitive window contents and input data. The attacker may also manipulate the forwarded session to some extent. The vulnerability does not affect availability and requires local access with user interaction. The CVSS score is 5.0 (medium severity).

Red Hat has released security updates that fix this vulnerability in OpenSSH packages for Red Hat Hardened Images and Red Hat Enterprise Linux 8. Users should apply the relevant updates as described in the Red Hat advisories RHSA-2026:36759 and RHSA-2026:47755. Patch status is confirmed with official fixes available. No additional mitigation steps are indicated by the vendor advisory.