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Full vulnerability report · 2026
CVE-2026-59849High confidence

Libssh: libssh: denial of service via automatic certificate authentication loop

Red Hat · Red Hat Enterprise Linux 10

Official source articles: Red Hat RHSA-2026:55855 ↗ · Red Hat RHSA-2026:42922 ↗. Check the applicable product and release in the original source.

3.1LowCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityLowOperational priority:Low, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 0.44% 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: No default targetRemediation target: Normal maintenance

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.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

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
Package result overrides the generic status

BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 1 affected package state shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.

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 · sourcelibsshVendor fix publishedDebian records a fixed source-package version for this release.0.11.5-0+deb13u1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcelibsshAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcelibsshVendor fix publishedDebian records a fixed source-package version for this release.0.12.1-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcelibsshVendor fix publishedDebian records a fixed source-package version for this release.0.12.1-1Debian Security Tracker ↗Source updated 5 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-2026-59849 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitylibssh: libssh: denial of service via automatic certificate authentication loop
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. 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.
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-2026-46263

No EUVD known-exploited evidence

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.

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
3.1 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

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.

What

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.

Why

A malformed condition prevents a loop from making progress or terminating, allowing resource exhaustion.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

What

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.

Why

A malformed condition prevents a loop from making progress or terminating, allowing resource exhaustion.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

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 → Loop with Unreachable Exit Condition ('Infinite Loop') → disrupt the affected service
Attack surface
Network
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
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-835 ↗

CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop'). The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.

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:H/PR:L/UI:N/S:U/C:N/I:N/A:L

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.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.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.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.ALowAvailability impact: A successful attack can cause a limited 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.
NetworkDenial of serviceCWE-835
A

Official authority intelligence

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

ENISA EUVD · EUVD-2026-46263Official EUVD mapping

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.

Official EUVD record ↗
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-2026-026175libssh等の複数ベンダの製品における無限ループに関する脆弱性

libsshに脆弱性が見つかりました。自動証明書ベースの公開鍵認証における論理エラーにより、設定された証明書が存在しない場合やサーバーにより繰り返し拒否された場合に、libsshクライアントが無限ループに陥り、サービス拒否が発生す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.
Fix availability varies by product
Affected
Fixed
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
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 19 Aug 2026, 04:57 UTC · CWE-835 · Loop with Unreachable Exit Condition ('Infinite Loop')

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-2026-46263
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched

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 vendor advisory: access.redhat.com/RHSA-2026:55855.
    Before
    remediation: access.redhat.com/RHSA-2026:42922 · vendor advisory: access.redhat.com/CVE-2026-59849 · vendor advisory: bugzilla.redhat.com/show_bug.cgi?id=2498182
    After
    remediation: access.redhat.com/RHSA-2026:42922 · vendor advisory: access.redhat.com/CVE-2026-59849 · vendor advisory: access.redhat.com/RHSA-2026:55855 · 1 more references
    secalert@redhat.com ↗
  2. Affected versionsThe structured affected or fixed version information changed.
    Before
    See the vendor and CVE records for the affected range. · Fixed: 0:0.12.0-3.el10_2 < *; 0.12.1-4.hum1 < *
    After
    See the vendor and CVE records for the affected range. · Fixed: Red Hat Enterprise Linux 10: 0:0.12.0-3.el10_2 < *; Red Hat Hardened Images: 0.12.1-4.hum1 < *
    CNA ↗
  3. 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-2026-59849 · 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-2026-59849 · vendor advisory: bugzilla.redhat.com/show_bug.cgi?id=2498182
    secalert@redhat.com ↗
  4. 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-2026-59849 · vendor advisory: bugzilla.redhat.com/show_bug.cgi?id=2498182
    After
    remediation: access.redhat.com/RHSA-2026:55855 · vendor advisory: access.redhat.com/CVE-2026-59849 · vendor advisory: access.redhat.com/RHSA-2026:55855 · 1 more references
    access.redhat.com ↗
  5. 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-2026-46263↗Vendor advisory↗Vendor advisory · Red Hat RHSA-2026:55855↗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-2026-59849 · cve.blacktree.nl