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libssh EUVDEUVD-2026-46178

| CVE-2026-59845 MEDIUM
Detection of Error Condition Without Action (CWE-390)
2026-07-21 redhat GHSA-97fp-2vw9-q5jg
Denial Of Service Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 9 Red Hat Hardened Images Red Hat
5.9
CVSS 3.1 · NVD
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Severity by source

Vendor (redhat) PRIMARY
MEDIUM
qualitative
NVD
5.9 MEDIUM
AV:L/AC:L/PR:L/UI:R/S:C/C:N/I:N/A:H
vuln.today AI
5.3 MEDIUM

ProxyCommand config and fork() failure both required (AC:H, AV:L); low-privileged local account and active SSH initiation needed (PR:L, UI:R); signal propagation beyond libssh to caller's process tree drives S:C with availability-only impact.

3.1 AV:L/AC:H/PR:L/UI:R/S:C/C:N/I:N/A:H
4.0 AV:L/AC:H/AT:P/PR:L/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
SUSE
6.5 MEDIUM
AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
Red Hat
5.3 MEDIUM
qualitative

Primary rating from Vendor (redhat).

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
Required
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

3
CVSS changed
Jul 30, 2026 - 13:22 NVD
5.3 (MEDIUM) 5.9 (MEDIUM)
Analysis Generated
Jul 21, 2026 - 12:03 vuln.today
CVE Published
Jul 21, 2026 - 11:26 cve.org
MEDIUM 5.3

DescriptionNVD

A flaw was found in libssh. When ProxyCommand is used, an unchecked fork() failure can be stored as process ID -1; during cleanup, signals may then be sent across the caller's accessible process tree, leading to local denial of service.

AnalysisAI

Signal misdelivery in libssh's ProxyCommand handling allows a low-privileged local user to trigger a local denial of service affecting their entire accessible process tree. When fork() fails during ProxyCommand execution, the error return value of -1 is stored unchecked as a child process ID; at cleanup, libssh signals PID -1, which Linux interprets as a broadcast to all processes the caller has permission to signal. No public exploit code has been identified at time of analysis, and the vulnerability is not listed in CISA's KEV catalog, but the CVSS scope-changed metric (S:C) confirms that impact extends beyond the libssh component itself to co-located user processes.

Technical ContextAI

libssh is an open-source C library implementing the SSH protocol, used by various applications for secure shell communications on Linux and other POSIX platforms. The ProxyCommand feature routes SSH connections through an intermediate shell command - commonly used for jump hosts or tunneling - and involves a fork() call to spawn a subprocess. POSIX specifies that fork() returns -1 on failure (e.g., when the system process table is exhausted or a per-user RLIMIT_NPROC limit is reached), but this error return is stored without validation as the child process ID. During session teardown or error cleanup, libssh issues a signal (e.g., SIGTERM/SIGKILL) to what it believes is the spawned child; Linux interprets kill(-1, sig) as a broadcast to every process the calling process has permission to signal - the entire reachable process tree of that user. The root cause is an unchecked error return value (closely related to CWE-252: Unchecked Return Value), though NVD has not assigned a formal CWE to this entry. Affected products are confirmed via CPE as libssh as packaged in Red Hat Enterprise Linux 8, 9, 10, and Hardened Images.

RemediationAI

No specific patched libssh package version is confirmed in the available data; monitor the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-59845 and the Bugzilla entry at https://bugzilla.redhat.com/show_bug.cgi?id=2498178 for errata providing fixed packages for RHEL 8, 9, 10, and Hardened Images - apply the errata update as soon as it is released. Until a patch is available, the most targeted compensating control is to remove or disable ProxyCommand directives from user-level SSH configurations (~/.ssh/config) and system-level configurations (/etc/ssh/ssh_config), since the vulnerability is entirely conditional on ProxyCommand being in use - eliminating this directive removes the vulnerable code path with no impact to standard SSH connections. The trade-off is loss of jump-host and connection-tunneling functionality. As a secondary hardening measure, enforcing per-user process limits via PAM (pam_limits, /etc/security/limits.conf) or cgroups to restrict RLIMIT_NPROC reduces the window during which fork() is likely to fail, decreasing the probability of accidental or induced triggering; however, this does not eliminate the flaw.

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Same weakness CWE-390 – Detection of Error Condition Without Action

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Same technique Denial Of Service

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Module for Basesystem 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Server for SAP Applications 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected

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EUVD-2026-46178 vulnerability details – vuln.today
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