CVE Intelligence
High Denial of service

CVE-2026-59849 — Libssh: libssh: denial of service via automatic certificate authentication loop

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.

Published Jul 21, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: redhat

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
—
No EPSS score.
Affects
Libssh
Libssh and 11 more
CVSS base
7.5
High · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Libssh Libssh, Red Hat Enterprise Linux, Red Hat Enterprise Linux For Els…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Search available logs for exploit probes matching the vulnerability class (denial of service), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Libssh Libssh ≥ 0.11.0 and < 0.11.5version 0.12.0 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux version 10.0version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Els version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Eus version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Ibm Z Systems version 10.0version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Ibm Z Systems Els version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Ibm Z Systems Eus version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Power Little Endian version 10.0version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Power Little Endian Els version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux For Power Little Endian Eus version 10.2 Vulnerable NIST National Vulnerability Database
Red Hat Hardened Images versions not specified by the source Vulnerable NIST National Vulnerability Database
Red Hat Hardened Images versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 10 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
7.5 CVSS 3.1 High 3.9 3.6 nvd@nist.gov via NIST National Vulnerability Database
3.1 CVSS 3.1 Low 1.6 1.4 secalert@redhat.com via NIST National Vulnerability Database
3.1 CVSS 3.1 Low — — redhat via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)
Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 7.5 (NVD (NIST)) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-835 · Infinite Loop

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Track CPU/memory spikes and availability drops correlated with request patterns.
web/proxy/WAF logsnetwork IDS/IPSresource metrics

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · red hat/red hat enterprise linux 10, red hat/red hat hardened images
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • CVSS changed · 7.5
    Oct 15, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVE published
    Jul 21, 2026 · redhat

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

4 on the record

Elsewhere on this site

Libssh
every CVE for this vendor
Denial of service
same class
CWE-835
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-110924 Openssh: openssh: gssapi delegated credentials can be stored after a failed authentication 8h
  • CVE-2026-110927 Openssh: openssh: a compressed payload can expand past the maximum packet size 8h
  • CVE-2026-110923 Openssh: openssh: sftp can write outside the destination directory from a server-supplied path 16h
  • CVE-2026-110926 Openssh: openssh: shared lz77 compression dictionary leaks plaintext across channels 16h
  • CVE-2026-110925 Openssh: openssh: '$' and '\' in a command-line username expand through %u 16h
  • CVE-2026-86849 Dpdk: dpdk: integer overflow combined with missing validation leads to host buffer overflow in vhost-crypto 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No FIRST EPSS score.
  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-59849 is "Libssh: libssh: denial of service via automatic certificate authentication loop", rated High. It affects Libssh (Libssh); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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