CVE Intelligence
Medium Memory corruption exploit reference

CVE-2023-25136 — OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms...

OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms handling. This is fixed in OpenSSH 9.2. The double free can be leveraged, by an unauthenticated remote attacker in the default configuration, to jump to any location in the sshd address space. One third-party report states "remote code execution is theoretically possible."

Published Feb 3, 2023 · Updated Oct 14, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: mitre

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
  • EPSS 89.7% (30-day exploitation probability)+15
  • Technical severity (medium)+3
  • CISA SSVC: exploitation "poc"+5

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
89.69%
ahead of 100% of scored CVEs · Oct 14, 2026
Affects
Fedoraproject
Fedora and 5 more
CVSS base
6.5
Medium · 2 source(s)
Prioritization reference: 9.8 provisional

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
Proof of concept
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.

  • Documented patch — ftp.openbsd.org (NIST National Vulnerability Database)
  • Documented patch — github.com (NIST National Vulnerability Database)

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 (Fedoraproject Fedora, Netapp 500f Firmware, Netapp A250 Firmware…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. EPSS ahead of 100% of scored CVEs: prioritize it in the patch queue.
  5. Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Fedoraproject Fedora version 37version 38 Vulnerable NIST National Vulnerability Database
Netapp 500f Firmware versions not specified by the source Vulnerable NIST National Vulnerability Database
Netapp A250 Firmware versions not specified by the source Vulnerable NIST National Vulnerability Database
Netapp C250 Firmware versions not specified by the source Vulnerable NIST National Vulnerability Database
Netapp Ontap Select Deploy Administration Utility versions not specified by the source Vulnerable NIST National Vulnerability Database
Openbsd Openssh version 9.1 Vulnerable NIST National Vulnerability Database

Attack characteristics

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

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
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
9.8 CVSS 3.1 Critical — — GitHub, Inc. via GitHub Security Advisories
6.5 CVSS 3.1 Medium 2.2 4.2 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H (score shown at the top: nvd@nist.gov)
Sources disagree significantly and the divergence is under review. Every score is kept with its origin. For prioritization we use 9.8 (GitHub, Inc. via GitHub Security Advisories) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-415 · Double Free

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).
  • Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

  • 2026
  • SSVC assessment updated
    Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 14, 2026
  • Fix documented
    Oct 14, 2026 · NIST National Vulnerability Database
  • Affected products added · openbsd/openssh, fedoraproject/fedora, netapp/ontap select deploy administration utility, netapp/a250 firmware, netapp/5
    Oct 14, 2026 · NIST National Vulnerability Database
  • CVSS changed · 6.5
    Oct 14, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 14, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 14, 2026 · Alertas do Telegram
  • 2023
  • CVE published
    Feb 3, 2023 · mitre

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 14, 2026 – Oct 14, 2026
  • 1× Official description updated · Oct 14, 2026 – Oct 14, 2026

References

25 on the record

Elsewhere on this site

Fedoraproject
every CVE for this vendor
Memory corruption
same class
CWE-415
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-106583 In ssh in OpenSSH before 10.6, a $ or \ character can occur in a command-line username, leading... 8d
  • CVE-2026-106588 In sshd in OpenSSH through 10.6, use of the macOS 27 (or later) SDK has the side effect… 8d
  • CVE-2026-106587 Type Confusion in Openbsd Openssh 8d
  • CVE-2026-106589 In sshd in OpenSSH through 10.6, in certain environments such as QNX 6 and SCO… 8d
  • CVE-2026-106555 Incorrect Resource Transfer Between Spheres in Openbsd Openssh 8d
  • CVE-2026-106582 In sshd and ssh in OpenSSH before 10.6, an LZ77 dictionary coder can be used even though… 8d

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 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-2023-25136 is "OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms...", rated Medium. It affects Fedora (Fedoraproject); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.5 describes technical severity. EPSS 89.69% estimates the probability of exploitation in 30 days; neither replaces your asset context. 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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