CVE-2026-55655 | Openssh: local mitm of x11 forwarding via abstract unix socket pre-binding in red hat enterprise linux openssh client versions

A flaw was found in OpenSSH. A local unprivileged attacker on a Linux client host can hijack client-side X11 forwarding connections. This is possible by pre-binding the preferred abstract X socket name when X11 forwarding is enabled and a local UNIX-domain X socket is used. A successful attack can compromise the confidentiality of forwarded X11 traffic, including sensitive window contents and input, and may allow some manipulation of the forwarded session.

Published: 2026-06-23 Last update: 2026-06-25 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-55655 is rated Low Risk (20.2/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.09%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-55655

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-23 — 0.09% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-55655

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.0 3.1 MEDIUM
CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 0.8 4.2 [email protected]
6.1 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 1.8 4.2 [email protected]

Weakness enumeration for CVE-2026-55655

GitHub Security Advisory for CVE-2026-55655

GHSA-wcvf-3x75-j4c6 · Severity: medium — A flaw was found in OpenSSH. A local unprivileged attacker on a Linux client host can hijack...

OS Trackers for CVE-2026-55655

vendor priority summary link
debian not yet assigned CVE-2026-55655 not yet assigned priority: Debian including 1 source packages (openssh), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): undetermined 5. https://security-tracker.debian.org/tracker/CVE-2026-55655
redhat medium — https://access.redhat.com/security/cve/CVE-2026-55655
ubuntu medium CVE-2026-55655 medium priority: Ubuntu including 2 source packages (openssh, openssh-ssh1), 16 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): deferred 8, ignored 7, needs-triage 1. https://ubuntu.com/security/CVE-2026-55655

Affected software / configurations for CVE-2026-55655

Vendor Product Version Raw CPE
openbsd openssh — cpe:2.3:a:openbsd:openssh:-:*:*:*:*:*:*:*
redhat enterprise_linux 6.0 cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*
redhat enterprise_linux 7.0 cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
redhat enterprise_linux 9.0 cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*
redhat enterprise_linux 10.0 cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:*

References for CVE-2026-55655

cvelogic Threat Intelligence