CVE-2026-55655

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.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

Security Fix(es):

• openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Rocky Linux OpenSSH client versions (CVE-2026-55655)

• openssh: Double free in Rocky Linux versions of OpenSSH DH-GEX client path during FIPS known-group validation leads to client-side denial of service (CVE-2026-55653)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

Security Fix(es):

• openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Rocky Linux OpenSSH client versions (CVE-2026-55655)

• openssh: Double free in Rocky Linux versions of OpenSSH DH-GEX client path during FIPS known-group validation leads to client-side denial of service (CVE-2026-55653)

• openssh: Heap out-of-bounds read in Rocky Linux versions of OpenSSH GSSAPI indicator cleanup due to missing NULL sentinel termination (CVE-2026-55654)

• openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side (CVE-2026-60002)

• openssh: OpenSSH: scp file misplacement vulnerability during remote copy (CVE-2026-59996)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

Security Fix(es):

• openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Rocky Linux OpenSSH client versions (CVE-2026-55655)

• openssh: Double free in Rocky Linux versions of OpenSSH DH-GEX client path during FIPS known-group validation leads to client-side denial of service (CVE-2026-55653)

• openssh: Heap out-of-bounds read in Rocky Linux versions of OpenSSH GSSAPI indicator cleanup due to missing NULL sentinel termination (CVE-2026-55654)

• openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side (CVE-2026-60002)

• openssh: OpenSSH: scp file misplacement vulnerability during remote copy (CVE-2026-59996)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

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.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

Security Fix(es):

• openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in AlmaLinux OpenSSH client versions (CVE-2026-55655)
• openssh: Double free in AlmaLinux versions of OpenSSH DH-GEX client path during FIPS known-group validation leads to client-side denial of service (CVE-2026-55653)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

Security Fix(es):

• openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in AlmaLinux OpenSSH client versions (CVE-2026-55655)
• openssh: Double free in AlmaLinux versions of OpenSSH DH-GEX client path during FIPS known-group validation leads to client-side denial of service (CVE-2026-55653)
• openssh: Heap out-of-bounds read in AlmaLinux versions of OpenSSH GSSAPI indicator cleanup due to missing NULL sentinel termination (CVE-2026-55654)
• openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side (CVE-2026-60002)
• openssh: OpenSSH: scp file misplacement vulnerability during remote copy (CVE-2026-59996)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

Security Fix(es):

• openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in AlmaLinux OpenSSH client versions (CVE-2026-55655)
• openssh: Double free in AlmaLinux versions of OpenSSH DH-GEX client path during FIPS known-group validation leads to client-side denial of service (CVE-2026-55653)
• openssh: Heap out-of-bounds read in AlmaLinux versions of OpenSSH GSSAPI indicator cleanup due to missing NULL sentinel termination (CVE-2026-55654)
• openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side (CVE-2026-60002)
• openssh: OpenSSH: scp file misplacement vulnerability during remote copy (CVE-2026-59996)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

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.

• CVE-2026-55655: gate the client-side abstract X11 socket behind SSH_INSECURE_ABSTRACT_SOCKET_ENABLED to prevent MITM of forwarded X11 via abstract UNIX socket pre-binding; backport downstream f5884eb

• CVE-2026-55655: gate the client-side abstract X11 socket behind SSH_INSECURE_ABSTRACT_SOCKET_ENABLED to prevent MITM of forwarded X11 via abstract UNIX socket pre-binding; backport downstream f5884eb

Local mitm of x11 forwarding via abstract unix socket pre-binding in Red Hat Enterprise Linux openssh client versions. (CVE-2026-55655) sftp in OpenSSH before 10.4 does not properly constrain the location of downloaded files when "sftp server:/path ." is used with an attacker-controlled server. (CVE-2026-59995) scp in OpenSSH before 10.4 may place a file in the parent directory of an intended directory when the copy occurs between two remote destinations. (CVE-2026-59996) internal-sftp in sshd in OpenSSH before 10.4 recognizes only the first 9 command-line arguments, which can be important if a later command-line argument would have helped to ensure the intended security properties of an SFTP connection. (CVE-2026-59997) sshd in OpenSSH before 10.4 has an undocumented security-relevant behavior: GSSAPIStrictAcceptorCheck has no value if the server is in Windows Active Directory. (CVE-2026-59998) In sshd in OpenSSH before 10.4, DisableForwarding=yes was supposed to take precedence over PermitTunnel=yes, but did not. (CVE-2026-59999) sshd in OpenSSH before 10.4 allows remote attackers to cause a denial of service (resource consumption from excessive authentication attempts) because MaxAuthTries was mishandled for GSSAPIAuthentication. (CVE-2026-60000) sshd in OpenSSH before 10.4 does not always honor the minimum authentication delay. (CVE-2026-60001) ssh in OpenSSH before 10.4 can have a use-after-free when a server changes its host key during a key re-exchange. (This outcome occurs only on the client side.). (CVE-2026-60002) In ssh-agent in OpenSSH before 10.5, some operations can occur remotely but were intended to occur only locally, including operations that add tokens or use keys. This is caused by misinteraction between agent locking and the [email protected] extension. (CVE-2026-73281) In ssh in OpenSSH before 10.5, a use-after-free for realloc data can occur if a certain pair of remote-forwarding operations are concurrent. (CVE-2026-73282) In sshd in OpenSSH before 10.5, the restrict keyword (in authorized_keys) was supposed to be applicable to tunnel forwarding but was not. (CVE-2026-73283) In sftp in OpenSSH before 10.6, a server can trigger directory traversal (causing files to be written to unintended locations) during a recursive copy operation. (CVE-2026-106552) In sshd in OpenSSH before 10.6, credentials can incorrectly persist after failure of a GSSAPIAuthentication authentication attempt. (CVE-2026-106553) In sshd in OpenSSH before 10.6, GSSAPIAuthentication authentication state can incorrectly be persisted across authentication attempts. (CVE-2026-106555) In sshd and ssh in OpenSSH before 10.6, an LZ77 dictionary coder can be used even though this is contraindicated by the arXiv 2609.07709 "Crossing the Streams" findings. (CVE-2026-106582) In ssh in OpenSSH before 10.6, a $ or \ character can occur in a command-line username, leading to injection. (CVE-2026-106583) In ssh-keygen in OpenSSH before 10.6, certificates could have incorrect expiration times because of Daylight Saving mishandling. There can be a slightly more severe effect on users in certain Antarctic locations. (CVE-2026-106584) In sshd and ssh in OpenSSH before 10.6, there is no check for whether the maximum packet length is exceeded during decompression of highly compressed data. (CVE-2026-106585) In sshd in OpenSSH before 10.6, the restrict keyword (in authorized_keys) was supposed to be applicable to tunnel forwarding but was not, a different vulnerability than CVE-2026-73283. (CVE-2026-106586) In sshd in OpenSSH before 10.6, the value "none" for a configuration option is sometimes interpreted as a filename but was intended to mean that a feature is disabled. (CVE-2026-106587)