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libssh CVE-2026-59849

| EUVDEUVD-2026-46263 HIGH
Loop with Unreachable Exit Condition (Infinite Loop) (CWE-835)
2026-07-21 redhat GHSA-jp6g-7mqj-wj53
Denial Of Service Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 9 Red Hat Hardened Images Red Hat
High
Disputed · 7.5 NVD
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Severity by source

Sources disagree (Low–High)
Vendor (redhat) PRIMARY
LOW
qualitative
NVD
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
5.3 MEDIUM

Client must be configured for certificate auth and must connect to a hostile/misconfigured server, so AC:H and UI:R; impact is availability-only (A:H) with no confidentiality or integrity effect.

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

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

6
Analysis Updated
Jul 30, 2026 - 16:45 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Jul 30, 2026 - 16:37 vuln.today
cvss_changed
Severity Changed
Jul 30, 2026 - 16:37 NVD
LOW HIGH
CVSS changed
Jul 30, 2026 - 16:37 NVD
3.1 (LOW) 7.5 (HIGH)
Analysis Generated
Jul 21, 2026 - 15:01 vuln.today
CVE Published
Jul 21, 2026 - 14:08 cve.org
LOW 3.1

DescriptionNVD

A flaw was found in libssh. Logic errors in automatic certificate-based public key authentication can cause libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected by a server, leading to denial of service.

AnalysisAI

Denial of service in libssh affects clients that use automatic certificate-based public key authentication, where logic errors cause the client to loop indefinitely when configured certificates are absent or are repeatedly rejected by the SSH server. Reported by Red Hat and shipped in Red Hat Enterprise Linux 8, 9, and 10 plus Red Hat Hardened Images, the flaw lets a hostile or misconfigured server hang a connecting client and consume CPU. There is no public exploit identified at time of analysis, and EPSS is low at 0.17% (7th percentile), consistent with an availability-only, client-side bug rather than a mass-exploited issue.

Technical ContextAI

libssh is a widely used C library implementing the SSHv2 protocol for both client and server roles, and is embedded in numerous applications and Linux distributions. This issue lives in its client-side automatic certificate-based public key authentication path, where SSH certificates (signed public keys) are offered to the server during the auth handshake. The root cause is CWE-835 (Loop with Unreachable Exit Condition, i.e. an infinite loop): the certificate-selection/retry logic lacks a correct termination condition, so when no valid certificate is available or the server keeps rejecting the offered certificate, the client re-enters the authentication attempt loop without progressing and spins indefinitely.

RemediationAI

Patch available per vendor advisory: apply the libssh update delivered in Red Hat errata RHSA-2026:42922 (https://access.redhat.com/errata/RHSA-2026:42922) for the affected RHEL 8, 9, and 10 streams and Red Hat Hardened Images, then restart or rebuild any services and containers that link libssh so the fixed library is loaded. Exact fixed version strings are not provided in the input data - confirm the target package version from RHSA-2026:42922 before deploying. As a temporary compensating control until patching, disable or avoid automatic certificate-based public key authentication in libssh clients and fall back to standard key or password authentication, since removing the certificate-auth trigger prevents the infinite loop; the trade-off is loss of SSH certificate-based authentication for those clients. Where feasible, restrict outbound SSH from libssh-based clients to trusted, known-good servers to limit exposure to hostile servers that could repeatedly reject certificates. Additional context is available in the oss-security advisory https://seclists.org/oss-sec/2026/q3/197 and https://vuldb.com/vuln/380927.

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Same weakness CWE-835 – Loop with Unreachable Exit Condition (Infinite Loop)

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Vendor StatusVendor

SUSE

Severity: Low
Product Status
SUSE Linux Enterprise Server 16.0 SUSE Linux Enterprise Server for SAP applications 16.0 Fixed
SUSE Linux Micro 6.2 Fixed
openSUSE Leap 16.0 Fixed
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected

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CVE-2026-59849 vulnerability details – vuln.today
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