A system is running a version of software that was replaced with a Trojan Horse at one of its distribution points, such as (1) TCP Wrappers 7.6, (2) util-linux 2.9g, (3) wuarchive ftpd (wuftpd) 2.2 and 2.1f, (4) IRC client (ircII) ircII 2.2.9, (5) OpenSSH 3.4p1, or (6) Sendmail 8.12.6.

Last updated 13 July 2026

Last updated 22 September 2026

In sshd in OpenSSH before 10.4, DisableForwarding=yes was supposed to take precedence over PermitTunnel=yes, but did not.

On July 1, 2024, the Qualys Threat Research Unit (TRU) disclosed an unauthenticated, remote code execution vulnerability that affects the OpenSSH server (sshd) in glibc-based Linux systems.CVE-2024-6387: A signal handler race condition was found in sshd, where a

In OpenSSH before 10.3, a file downloaded by scp may be installed setuid or setgid, an outcome contrary to some users' expectations, if the download is performed as root with -O (legacy scp protocol) and without -p (preserve mode).

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.)

The PKCS#11 feature in ssh-agent in OpenSSH before 9.3p2 has an insufficiently trustworthy search path, leading to remote code execution if an agent is forwarded to an attacker-controlled system. (Code in /usr/lib is not necessarily safe for loading into ssh-agent.) NOTE: this issue exists because of an incomplete fix for CVE-2016-10009.

Last updated 22 September 2026

Last updated 22 September 2026

Last updated 22 September 2026

OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kexalgorithms handling. This is fixed in OpenSSH 9.2. The double free can be leveraged, by an unauthenticated remote attacker in the default configuration, to jump to any location in the sshd address space. One third-party report states "remote code execution is theoretically possible."

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.

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.

Last updated 13 July 2026

Last updated 22 September 2026

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.

ssh in OpenSSH before 10.1 allows the '\0' character in an ssh:// URI, potentially leading to code execution when a ProxyCommand is used.

In sshd in OpenSSH before 10.0, the DisableForwarding directive does not adhere to the documentation stating that it disables X11 and agent forwarding.

scp in OpenSSH through 8.3p1 allows command injection in scp.c remote function, as demonstrated by backtick characters in the destination argument. NOTE: the vendor reportedly has stated that they intentionally omit validation of "anomalous argument transfers" because that could "stand a great chance of breaking existing workflows."

Reference: https://www.openssh.com/security.html

The OpenSSH client is vulnerable to an active machine-in-the-middle attack if the VerifyHostKeyDNS option is enabled (it is disabled by default): when a vulnerable client connects to a server, an active machine-in-the-middle can impersonate the server by completely bypassing the client's checks of the server's identity.

The OpenSSH client and server are vulnerable to a pre-authentication denial-of-service attack: an asymmetric resource consumption of both memory and CPU.

ssh in OpenSSH before 10.1 allows the '\0' character in an ssh:// URI, potentially leading to code execution when a ProxyCommand is used.

ssh in OpenSSH before 10.1 allows control characters in usernames that originate from certain possibly untrusted sources, potentially leading to code execution when a ProxyCommand is used. The untrusted sources are the command line and %-sequence expansion of a configuration file. (A configuration file that provides a complete literal username is not categorized as an untrusted source.)

The API function sshgethexa() is vulnerable, when 0-lenght input is provided to this function. This function is used internally in sshgetfingerprinthash() and sshprinthexa() (deprecated), which is vulnerable to the same input (length is provided by the calling application).

The function is also used internally in the gssapi code for logging the OIDs received by the server during GSSAPI authentication. This could be triggered remotely, when the server allows GSSAPI authentication and logging verbosity is set at least to SSHLOGPACKET (3). This could cause self-DoS of the per-connection daemon process.

A malicious SCP server can send unexpected paths that could make the client application override local files outside of working directory. This could be misused to create malicious executable or configuration files and make the user execute them under specific consequences.

This is the same issue as in OpenSSH, tracked as CVE-2019-6111.

OpenSSH before 10.3 mishandles the authorizedkeys principals option in uncommon scenarios involving a principals list in conjunction with a Certificate Authority that makes certain use of comma characters.

AIONLYREPORT package: openssh-9.9p1-22.el102 ------ Summary: Local MITM of X11 forwarding via preferred Linux abstract UNIX socket connection: a local unprivileged process on the Linux client host can hijack the client-side X11 forwarding connection by pre-binding the preferred abstract X socket name. Requirements to exploit: An attacker needs local unprivileged code execution on the Linux host running the OpenSSH client, client-side X11 forwarding enabled (-X, -Y, or equivalent configuration), a local DISPLAY that resolves to a UNIX-domain X socket such as :0 or unix:0, and a forwarded X11 connection to be opened while the attacker has pre-bound the matching abstract socket name. Component affected: openssh-9.9p1-22.el102, client-side X11 forwarding code in openssh-9.9p1/channels.c (connectlocalxsocket(), x11openhelper()). Version affected: openssh-9.9p1-22.el102; reachable on Linux in the client-side X11 forwarding path when X11 forwarding is enabled and DISPLAY resolves to a local UNIX-domain X socket Patch available: no released package fix established; proposed patch included below Version fixed: unknown Upstream coordination: Not notified. CVSS: CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N - 5.3 (MEDIUM) AV:L - The attacker must already have local code execution on the Linux system running the OpenSSH client. AC:H - Exploitation depends on a feature-specific client configuration, successful pre-binding of the matching abstract X11 socket, and a forwarded X11 connection actually being opened. PR:L - An unprivileged local user account or equivalent local process execution is sufficient. UI:R - A user must enable X11 forwarding and the session must trigger a forwarded X11 connection. S:U - The impact stays within the client-side OpenSSH/X11 forwarding security scope. C:H - A successful hijack can expose forwarded X11 traffic, including sensitive window contents and input; when real xauth data is available, the saved X11 authentication data may also be substituted into the hijacked stream. I:L - The attacker can influence the X11 protocol stream presented to the forwarded application, but the demonstrated effect is narrower than general host compromise. A:N - The issue does not require a direct availability impact to succeed. Impact: Moderate. A successful attack can compromise the confidentiality of forwarded X11 traffic and allow some integrity impact on the forwarded session, but exploitation is limited to a local attacker on the client host and depends on the non-default, feature-specific condition that X11 forwarding is enabled and used. Under Red Hat’s criteria, this is better classified as Moderate than Important because it is real but not easily exploitable in typical deployments. Embargo: no Reason: This is a local, configuration-dependent client-side issue with straightforward mitigation by disabling X11 forwarding where it is not required, and it does not present an easily exploitable remote compromise path. Acknowledgement: Aisle Research Vulnerability Details: This issue is in the OpenSSH client’s Linux X11 forwarding path. When the client receives an X11 open request, the call path reaches x11connectdisplay(), which parses DISPLAY and, for local UNIX-domain displays such as :0 or unix:0, calls connectlocalxsocket(). In the vulnerable path, Linux tries the abstract UNIX socket name before the filesystem socket: c len = snprintf(buf + 1, sizeof (buf) - 1, PATHUNIXX, dnr); #ifdef linux / try abstract socket first / buf[0] = '\0'; if ((ret = connectlocalxsocketpath(buf, len + 1)) >= 0) return ret; #endif if ((ret = connectlocalxsocketpath(buf + 1, len)) >= 0) return ret; PATHUNIXX resolves to /tmp/.X11-unix/X%u, so on Linux the first attempted endpoint is the abstract socket name \0/tmp/.X11-unix/X<display>. Because Linux abstract UNIX sockets are not mediated by filesystem permissions, an unprivileged local process can pre-bind that name and receive the forwarded X11 connection before the legitimate filesystem socket. The connection helper performs a direct connect() and does not verify peer credentials or ownership after the connection succeeds. OpenSSH’s X11 spoofing logic validates the fake cookie received from the remote side, but it does not authenticate the local X11 endpoint. After the fake cookie check passes, the client replaces it with the saved X11 authentication data: c if (datalen != sc->x11fakedatalen || timingsafebcmp(ucp + 12 + ((protolen + 3) & ~3), sc->x11fakedata, sc->x11fakedatalen) != 0) { debug2("X11 auth data does not match fake data."); return -1; } ... memcpy(ucp + 12 + ((protolen + 3) & ~3), sc->x11saveddata, sc->x11saveddatalen); As a result, an attacker-controlled abstract socket can receive the forwarded X11 session first. Where real xauth data was obtained, the rewritten first packet will contain the saved X11 authentication data. If xauth data is unavailable, OpenSSH can fall back to generated fake data, which reduces credential-leak impact but does not prevent the connection hijack or interception of the forwarded X11 stream. The available evidence supports interception and limited manipulation of forwarded X11 sessions, not arbitrary code execution or privilege escalation in the client itself. Steps to reproduce: 1. On a Linux system running the OpenSSH client, confirm the local display uses a UNIX-domain socket such as :0 or unix:0. 2. Before opening a forwarded X11 connection, start a local unprivileged listener bound to the matching abstract socket name. For display :0: python import socket s = socket.socket(socket.AFUNIX, socket.SOCKSTREAM) s.bind("\0/tmp/.X11-unix/X0") s.listen(1) c, = s.accept() print("accepted; first bytes:", c.recv(64).hex()) 3. In another terminal, start an SSH session with X11 forwarding enabled: bash ssh -X user@remote 4. From the remote shell, trigger an X11 application so that the client opens the forwarded X11 channel, for example: bash xclock 5. Observe that the attacker listener accepts the connection and receives the initial X11 bytes before the legitimate filesystem socket /tmp/.X11-unix/X0 is used. 6. Optional confirmation: bash strace -f -e connect ssh -X user@remote Expected result: tracing shows a successful AFUNIX connect to the abstract socket name \0/tmp/.X11-unix/X0 before any successful connect to /tmp/.X11-unix/X0. Mitigation: Disable X11 forwarding on affected clients when it is not required, for example by avoiding -X/-Y and using ForwardX11 no. On shared Linux systems where untrusted local users or processes may be present, avoid relying on client-side X11 forwarding until a fix that prefers the filesystem X socket has been applied. Proposed Fix: Prefer the filesystem X11 socket first, and retain Linux abstract sockets only as a compatibility fallback. diff diff --git a/openssh-9.9p1/channels.c b/openssh-9.9p1/channels.c @@ static int connectlocalxsocket(uint dnr) len = snprintf(buf + 1, sizeof (buf) - 1, PATHUNIXX, dnr); + / Prefer filesystem socket (permission/ownership mediated) / + if ((ret = connectlocalxsocketpath(buf + 1, len)) >= 0) + return ret; #ifdef linux - / try abstract socket first / + / Abstract socket fallback for compatibility / buf[0] = '\0'; if ((ret = connectlocalxsocketpath(buf, len + 1)) >= 0) return ret; #endif - if ((ret = connectlocalxsocketpath(buf + 1, len)) >= 0) - return ret; error("connect %.100s: %.100s", buf + 1, strerror(errno)); return -1; ------ This report was generated using AI technology. Always review AI-generated content prior to use

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.

If PAM is configured to read user-specified environment variables and UseLogin=yes in sshdconfig, then a hostile local user may attack /bin/login via LDPRELOAD or similar environment variables set via PAM.

Upstream fix:

https://anongit.mindrot.org/openssh.git/commit/?id=85bdcd7c92fe7ff133bbc4e10a65c91810f88755

Debian advisory:

https://www.debian.org/security/2016/dsa-3550