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libssh CVE-2026-59851

| EUVDEUVD-2026-46268 HIGH
Incorrect Authorization (CWE-863)
2026-07-21 redhat GHSA-x5cr-v39m-53gw
8.8
CVSS 3.1 · Vendor: redhat
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Severity by source

Vendor (redhat) PRIMARY
8.8 HIGH
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
8.8 HIGH

Network-reachable and low-complexity once authenticated (AV:N/AC:L); a valid Kerberos principal is required (PR:L); logging in as arbitrary users yields full C:H/I:H/A:H on the host with no scope change.

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

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

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

Lifecycle Timeline

2
Analysis Generated
Jul 21, 2026 - 15:02 vuln.today
CVE Published
Jul 21, 2026 - 14:20 cve.org
HIGH 8.8

DescriptionCVE.org

A flaw was found in libssh. On servers with GSSAPIKeyExchange enabled, the gssapi-keyex path does not verify whether the authenticated Kerberos principal is authorized for the requested local user, allowing authenticated clients to log in as arbitrary users.

AnalysisAI

Privilege escalation via authentication bypass in libssh affects servers that enable GSSAPIKeyExchange, where the gssapi-keyex authentication path fails to confirm that the authenticated Kerberos principal is actually authorized for the local user account being requested. An already-authenticated client holding any valid Kerberos principal in the realm can therefore log in as an arbitrary user, including potentially privileged accounts, on Red Hat Enterprise Linux 8, 9, and 10 and Red Hat Hardened Images. No public exploit is identified at time of analysis and the issue is not listed in CISA KEV, but the CVSS of 8.8 reflects a straightforward, low-complexity abuse once a valid Kerberos credential is held.

Technical ContextAI

libssh is a widely used C library implementing the SSHv2 protocol for both client and server roles (distinct from the unrelated libssh2). The flaw lives in its GSSAPI/Kerberos key-exchange authentication method, gssapi-keyex, which is only reachable when the server is configured with GSSAPIKeyExchange enabled. Per CWE-863 (Incorrect Authorization), the code performs authentication (proving who the Kerberos principal is) but omits the authorization step that binds that principal to the specific local username requested in the SSH login. The missing check is analogous to the k5login/GSSAPI-to-local-user mapping that must gate which principals may assume which accounts; without it, any valid principal is accepted for any requested user. The affected products per CPE are Red Hat Enterprise Linux 8, 9, and 10 and Red Hat Hardened Images, all shipping the vulnerable libssh build.

RemediationAI

Apply the Red Hat libssh security update for your RHEL 8, 9, or 10 release or Red Hat Hardened Image; exact fixed version numbers are not included in the provided data, so obtain them from the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-59851 and the Bugzilla tracker at https://bugzilla.redhat.com/show_bug.cgi?id=2498184 rather than assuming a version. As the most effective compensating control until patched, disable GSSAPIKeyExchange on affected SSH servers (set GSSAPIKeyExchange no), which fully removes the vulnerable gssapi-keyex code path; the trade-off is loss of GSSAPI/Kerberos key-exchange single sign-on, so environments relying on it for passwordless Kerberos SSH will need to fall back to gssapi-with-mic or standard authentication. Where GSSAPI must remain, restrict network reachability of the SSH service to trusted management networks and tightly control which Kerberos principals are provisioned so the pool of potential abusers is minimized. Patch status: released patched version not independently confirmed from the provided references.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Micro 5.3 Affected
SUSE Linux Enterprise Micro 5.4 Affected
SUSE Linux Enterprise Micro 5.5 Affected

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CVE-2026-59851 vulnerability details – vuln.today

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