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Libssh Fixes Authentication Bypass and Multiple High-Impact Flaws

Vulnerability Disclosure · 2 sources · Updated 3mo ago · First seen Jul 21, 2026

Libssh released versions 0.12.1 and 0.11.5 to fix multiple security issues, including CVE-2026-59851, an authentication bypass in deployments where GSSAPIKeyExchange is enabled on servers. The flaw allows an authenticated client to log in as an arbitrary local user because the gssapi-keyex path fails to verify whether the authenticated Kerberos principal is authorized for the requested account. The vulnerability is tracked as CWE-863 and carries a CVSS v3.1 score reflecting high impact to confidentiality, integrity, and availability.

The 0.12.1 release addresses 11 CVEs, while 0.11.5 backports fixes for 8 CVEs affecting the 0.11 branch. In addition to the authentication bypass, the updates remediate a stack buffer overflow, information disclosure bugs, several denial-of-service conditions, a use-after-free issue, and an integrity downgrade flaw, alongside hardening changes such as zero-initializing ssh_string objects and validating peer public keys during Diffie-Hellman key exchange. Red Hat reported RHEL 8 and RHEL 9 as unaffected by CVE-2026-59851, listed RHEL 10 status as unknown, and marked Red Hat Hardened Images as affected for libssh and libssh2 package entries.

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Event timeline

How this story unfolded

Events from the most recent confirmed update back to the earliest known activity.

1 event · Jul 21, 2026

Jul 21, 20263mo ago
libssh releases versions 0.12.1 and 0.11.5 with security fixes
On July 21, 2026, libssh announced security releases 0.12.1 and 0.11.5 to address multiple vulnerabilities and security-relevant bugs. Version 0.12.1 fixes 11 CVEs and version 0.11.5 backports fixes for 8 CVEs affecting the 0.11 branch, including an authentication bypass issue tracked as CVE-2026-59851.
oss-sec: libssh 0.12.1 and 0.11.5 security releases

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Vulnerabilities

11 linked

Stack buffer overflow in libssh SFTP server longname construction (CVE-2026-15370)Heap out-of-bounds read in libssh GSSAPI Curve25519 key exchange (CVE-2026-59842)Local denial of service in libssh ProxyCommand fork failure handling (CVE-2026-59845)libssh Infinite-Loop Denial of Service via Zero Channel Packet Size (CVE-2026-59843)Authenticated memory-exhaustion DoS in libssh SFTP server (CVE-2026-59844)libssh SFTP Client Memory Exhaustion via Unknown Request IDs (CVE-2026-59848)AES-GCM Integrity Verification Bypass in libssh OpenSSL Backend (CVE-2026-59847)Shell Metacharacter Injection in libssh ProxyCommand Username Expansion (CVE-2026-59846)libssh GSSAPIKeyExchange Authorization Bypass (CVE-2026-59851)Use-after-free in libssh post-close channel data callbacks (CVE-2026-59850)+1 more

Organizations

1 linked

Libssh

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Source coverage

Sources

2 references tracked. Mallory keeps watching after this page renders.

Cvefeed High SeverityAdvisories · Jul 21, 2026

CVE-2026-59851 - Libssh: libssh: authentication bypass via missing gssapi principal checkOpen source ↗

Oss Security Mailing ListNews · Jul 21, 2026

oss-sec: libssh 0.12.1 and 0.11.5 security releasesOpen source ↗

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Libssh Fixes Authentication Bypass and Multiple High-Impact Flaws

How this story unfolded

libssh releases versions 0.12.1 and 0.11.5 with security fixes

Related entities

Vulnerabilities

Organizations

Sources

See the full picture, correlated to your attack surface.

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Libssh Fixes Authentication Bypass and Multiple High-Impact Flaws

How this story unfolded

libssh releases versions 0.12.1 and 0.11.5 with security fixes

Related entities

Vulnerabilities

Organizations

Sources

See the full picture, correlated to your attack surface.

Related stories

Critical libssh2 Flaws Expose SSH Clients to RCE, DoS, and Memory Disclosure

libssh2 Pre-Auth RCE Publicly Disclosed With Active Exploitation Claims

OpenSSH fixes MITM and pre-authentication DoS flaws in CVE-2025-26465 and CVE-2025-26466