Last updated 22 September 2026

AIONLYREPORT package: openssh-10.2p1-10.1.hum1 ------ Summary: Heap out-of-bounds read in GSSAPI indicator cleanup: missing trailing NULL termination in the GSSAPI auth-indicators array allows sentinel-based consumers to read past the allocated pointer array and may trigger an invalid free during cleanup. Requirements to exploit: An attacker needs network access to SSH on openssh-10.2p1-10.1.hum1 built with GSSAPI support and deployed with GSSAPIAuthentication yes; in this tree that option defaults to disabled. The Kerberos environment must provide a ticket containing at least one authenticated auth-indicators value, and execution must then reach either the failed sshgssapiuserok() cleanup path or the GSSAPIIndicators matching path. Component affected: openssh-10.2p1-10.1.hum1, server-side GSSAPI authentication code in gss-serv.c (sshgssapigetindicators()), with sentinel-based consumption in gss-serv.c (sshgssapiuserok()) and gss-serv-krb5.c (sshgssapicheckindicators()) Version affected: openssh-10.2p1-10.1.hum1 when built with GSSAPI support; remote triggerability additionally requires GSSAPIAuthentication yes and a Kerberos deployment that supplies authenticated auth-indicators Patch available: no released package fix established; proposed patch included below Version fixed: unknown Upstream coordination: Not yet established. CVSS: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L - 3.7 (LOW) AV:N - the vulnerable path is reachable through network SSH authentication traffic. AC:H - exploitation depends on a GSSAPI-enabled build, GSSAPIAuthentication yes, a Kerberos ticket carrying authenticated auth-indicators, and reaching a sentinel-based consumer path. PR:N - no prior privileges on the target host are required beyond initiating the SSH authentication exchange. UI:N - no separate user interaction is required once the target is configured this way. S:U - the effect is limited to the vulnerable SSH authentication component. C:N - no reliable confidentiality impact is established from the available evidence. I:N - no integrity impact is established from the available evidence. A:L - the demonstrated consequence is limited to out-of-bounds reads that may crash or abort the affected authentication path. Impact: Moderate. Red Hat classifies easily triggered remote denial of service issues as Important, but the trigger conditions here are materially narrower: the issue depends on GSSAPI support, non-default SSH configuration, Kerberos indicator issuance, and a specific authentication control flow. The demonstrated impact is limited to availability loss in privileged authentication code, so Moderate is a better fit than Important, while remaining above Low because the out-of-bounds iteration is concrete rather than merely theoretical. Embargo: no Reason: The issue is configuration-dependent, the demonstrated impact is limited to availability, and the proposed fix is small and low-risk. A normal public fix cycle appears more appropriate than an embargo. Acknowledgement: Aisle Research Vulnerability Details: In sshgssapigetindicators(), the client->indicators array is reallocated from count to count + 1 elements and the newly added slot is immediately filled with a newly allocated string: c client->indicators = xrecallocarray(client->indicators, count, count + 1, sizeof(char)); if (client->indicators == NULL) { fatal("sshgssapigetindicators failed to allocate memory"); } client->indicators[count] = xmalloc(value.length + 1); memcpy(client->indicators[count], value.value, value.length); client->indicators[count][value.length] = '\0'; count++; In this source tree, xrecallocarray() wraps recallocarray(), which zeroes only the newly added region when the allocation grows. Here the newly added region is exactly one pointer wide, and that pointer is overwritten before count is incremented. As a result, once at least one authenticated indicator is collected, there is no guaranteed trailing NULL entry after the last valid element even though later code relies on sentinel termination. Two consumers iterate until NULL: c if (gssapiclient.indicators != NULL) { for (i = 0; gssapiclient.indicators[i] != NULL; i++) free(gssapiclient.indicators[i]); free(gssapiclient.indicators); } c for (i = 0; client->indicators[i] != NULL; i++) { ret = matchpatternlist(client->indicators[i], options.gssindicators, 1); ... } These loops may read beyond the allocated pointer array while searching for a terminator. On the sshgssapiuserok() failure cleanup path, that out-of-bounds read may also cause free() to be called on a non-owned pointer if adjacent heap contents are interpreted as another indicator entry. Based on the available evidence, the established security consequence is an availability problem; reliable confidentiality or integrity impact is not demonstrated. Steps to reproduce: 1. Build openssh-10.2p1-10.1.hum1 with GSSAPI support and memory sanitizers such as ASan/UBSan. 2. Run sshd with GSSAPIAuthentication yes. 3. Authenticate with a Kerberos ticket that contains at least one authenticated auth-indicators name attribute. 4. Trigger a sentinel-based consumer by either causing sshgssapiuserok() to return false, for example through principal-to-local-user authorization failure, or by configuring GSSAPIIndicators so sshgssapicheckindicators() iterates the list. 5. Observe a sanitizer-reported read past the end of the indicators pointer array; depending on heap layout, cleanup may also attempt to free a non-owned pointer. Mitigation: Disabling GSSAPIAuthentication removes the remotely reachable path. If GSSAPI authentication is required, avoiding GSSAPIIndicators removes one consumer but does not remove the cleanup path after sshgssapiuserok() failure; the safer temporary mitigation is to restrict or disable use of Kerberos tickets carrying authenticated auth-indicators values until a fix is deployed. Proposed Fix: Ensure sshgssapigetindicators() leaves a dedicated trailing NULL slot after indicator collection so all sentinel-based consumers remain within bounds. diff diff --git a/gss-serv.c b/gss-serv.c @@ done: - / slot [count] is zeroed by recallocarray, serves as NULL sentinel / + / + Ensure a trailing NULL sentinel for sentinel-based consumers. + / + if (client->indicators != NULL) + client->indicators = xrecallocarray(client->indicators, + count, count + 1, sizeof(char )); ------ This report was generated using AI technology. Always review AI-generated content prior to use

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.

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 session-bind@openssh.com extension.

In sshd in OpenSSH before 10.5, the restrict keyword (in authorizedkeys) was supposed to be applicable to tunnel forwarding but was not.

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).

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.

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

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 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.

Last updated 13 July 2026

Last updated 13 July 2026

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.

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.)

Last updated 22 September 2026

In OpenSSH before 10.3, command execution can occur via shell metacharacters in a username within a command line. This requires a scenario where the username on the command line is untrusted, and also requires a non-default configurations of % in sshconfig.

OpenSSH before 10.3 can use unintended ECDSA algorithms. Listing of any ECDSA algorithm in PubkeyAcceptedAlgorithms or HostbasedAcceptedAlgorithms is misinterpreted to mean all ECDSA algorithms.

OpenSSH before 10.3 omits connection multiplexing confirmation for proxy-mode multiplexing sessions.

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.

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.

The function matchpattern() is used to match conditionals in client configuration files or known hosts against the hostname the client is connecting to.

When the configuration file or knownhosts file is controlled by the attacker, connecting to specific hostnames could cause timeouts and resource exhaustion due to the ineffective backtracking of complex regular expressions.

The pattern matching was modified to avoid the needless backtracing.

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.)

Last updated 22 September 2026

Last updated 22 September 2026

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.

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

Last updated 22 September 2026