CVE-2026-55655
MediumCVSS 5.0Exploitation Probability (EPSS)
Low risk0th percentile - higher than 0% of all known CVEs
Summary
A flaw in OpenSSH allows a local unprivileged attacker to hijack forwarded X11 connections. The attack pre-binds the preferred abstract X socket name when X11 forwarding is enabled and a local UNIX-domain socket is used. A successful attack can compromise the confidentiality of forwarded X11 traffic, including sensitive window contents and input.
Risk Assessment
The organization risks exposure of confidential data displayed in X11 windows and potential manipulation of the forwarded SSH session. An attacker can intercept window content and user input, posing a serious threat to information security.
Recommendation
Immediately update OpenSSH to the latest patched version. As a workaround, consider disabling X11 forwarding (X11Forwarding no) or restricting access for unprivileged users until the update is applied.
Other vulnerabilities in OpenSSH
See all- CVE-2016-6515High
The auth_password function in sshd in OpenSSH before version 7.3 does not limit password lengths for authentication, allowing remote attackers to cause a denial of service via long strings.
- CVE-2015-8325High
The do_setup_env function in sshd in OpenSSH through 7.2p2, when the UseLogin feature is enabled and PAM is configured to read .pam_environment files in user home directories, allows local users to gain privileges by triggering a crafted environment for the /bin/login program.
- CVE-2015-5600High
The kbdint_next_device function in auth2-chall.c in sshd in OpenSSH through 6.9 does not properly restrict the processing of keyboard-interactive devices within a single connection. This allows remote attackers to conduct brute-force attacks or cause denial of service via a long and duplicative list in the ssh -oKbdInteractiveDevices option.
- CVE-2014-1692High
The hash_buffer function in schnorr.c in OpenSSH through 6.4, when Makefile.inc is modified to enable the J-PAKE protocol, does not initialize certain data structures. This may allow remote attackers to cause a denial of service (memory corruption) or have unspecified other impact via vectors that trigger an error condition.
- CVE-2025-32728Medium
In sshd in OpenSSH before version 10.0, the DisableForwarding directive does not adhere to documentation, failing to disable X11 and agent forwarding.
- CVE-2026-39832Critical
When adding a key to a remote agent, constraint extensions such as [email protected] were not serialized in the request. Destination restrictions were silently stripped when forwarding keys, allowing unrestricted use of the key on the remote host.
- CVE-2026-39831Critical
Vulnerability in the Verify() method for FIDO/U2F security keys ([email protected], [email protected]) – the User Presence flag was not checked. Signatures generated without physical touch were accepted, allowing unauthorized use of the key.
- CVE-2025-26466Medium
A flaw in the OpenSSH package causes each received ping packet to allocate a pong packet in memory, stored in a queue until key exchange completes. A malicious client can send such packets continuously, leading to uncontrolled memory consumption on the server.
- CVE-2025-26465Medium
A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key.
- CVE-2023-28531Critical
The vulnerability in ssh-add in OpenSSH before 9.3 adds smartcard keys to ssh-agent without the intended per-hop destination constraints. The earliest affected version is 8.9.
Original NVD description (English source)
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.