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Full vulnerability report · 2026
CVE-2026-59851High confidence

Libssh: libssh: authentication bypass via missing gssapi principal check

Red Hat · Red Hat Enterprise Linux 10

Official source article: Red Hat RHSA-2026:42922 ↗. Check the applicable product and release in the original source.

8.8HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:High, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 0.49% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Red Hat Red Hat Enterprise Linux 10 and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 30 daysRemediation target: Within 180 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

4 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcelibsshNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcelibsshNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcelibsshVendor fix publishedDebian records a fixed source-package version for this release.0.12.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcelibsshVendor fix publishedDebian records a fixed source-package version for this release.0.12.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-59851 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitylibssh: libssh: authentication bypass via missing GSSAPI principal check
30 fixed

The vendor explicitly identifies these products or versions as containing the fix.

  • libssh-debuginfo-0:0.12.0-3.el10_2.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-debuginfo-0:0.12.0-3.el10_2.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-debuginfo-0:0.12.0-3.el10_2.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-debuginfo-0:0.12.0-3.el10_2.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-debugsource-0:0.12.0-3.el10_2.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-debugsource-0:0.12.0-3.el10_2.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-debugsource-0:0.12.0-3.el10_2.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-debugsource-0:0.12.0-3.el10_2.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-devel-0:0.12.0-3.el10_2.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-devel-0:0.12.0-3.el10_2.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-devel-0:0.12.0-3.el10_2.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10)
  • libssh-devel-0:0.12.0-3.el10_2.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10)
Summary
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.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-46268

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

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.

What

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.

Why

The application performs an authorisation check, but it does not correctly enforce the required permission boundary.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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.

Why

The application performs an authorisation check, but it does not correctly enforce the required permission boundary.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Incorrect Authorization → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-863 ↗

CWE-863: Incorrect Authorization. The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkCWE-863
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-2428libssh: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in libssh ausnutzen, um erweiterte Berechtigungen zu erlangen, Sicherheitsmaßnahmen zu umgehen, vertrauliche Informationen offenzulegen, einen Denial-of-Service-Angriff auszulösen und Daten zu manipulieren.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260722Security Bulletin 22 Jul 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 22 Jul 2026, published on 22 July 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-026173libssh等の複数ベンダの製品における不正な認証に関する脆弱性

libsshに脆弱性が見つかりました。GSSAPIKeyExchangeが有効になっているサーバーでは、gssapi-keyexパスが認証されたKerberosプリンシパルが要求されたローカルユーザーに対して認可されているかどうかを検証しません。そのため、認証されたクライアントが任意のユーザーとしてログインできる可能性があります。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
See the vendor and CVE records for the affected range.
Fixed
Action
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 21 Jul 2026 · Last source change 17 Aug 2026, 21:38 UTC · CWE-863 · Incorrect Authorization

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-46268
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Missing structured fields: affected versions. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: added remediation: access.redhat.com/RHSA-2026:42922; removed remediation: access.redhat.com/RHSA-2026:55855; removed vendor advisory: access.redhat.com/RHSA-2026:55855.
    Before
    remediation: access.redhat.com/RHSA-2026:55855 · vendor advisory: access.redhat.com/CVE-2026-59851 · vendor advisory: access.redhat.com/RHSA-2026:55855 · 1 more references
    After
    remediation: access.redhat.com/RHSA-2026:42922 · vendor advisory: access.redhat.com/CVE-2026-59851 · vendor advisory: bugzilla.redhat.com/show_bug.cgi?id=2498184
    secalert@redhat.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added remediation: access.redhat.com/RHSA-2026:55855; added vendor advisory: access.redhat.com/RHSA-2026:55855; removed remediation: access.redhat.com/RHSA-2026:42922.
    Before
    remediation: access.redhat.com/RHSA-2026:42922 · vendor advisory: access.redhat.com/CVE-2026-59851 · vendor advisory: bugzilla.redhat.com/show_bug.cgi?id=2498184
    After
    remediation: access.redhat.com/RHSA-2026:55855 · vendor advisory: access.redhat.com/CVE-2026-59851 · vendor advisory: access.redhat.com/RHSA-2026:55855 · 1 more references
    access.redhat.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    See the vendor and CVE records for the affected range. · Fixed: 0.12.1-4.hum1 < *
    After
    See the vendor and CVE records for the affected range. · Fixed: 0:0.12.0-3.el10_2 < *; 0.12.1-4.hum1 < *
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-46268↗Vendor advisory↗Vendor advisory↗CVE authority or vendor reference · Red Hat RHSA-2026:42922↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-59851 · cve.blacktree.nl