CVE-2023-25136Public exploitNetwork attack vector

Pre-auth child-process crash via double free

Published Feb 3, 2023 · Updated May 28, 2026

Double free in OpenSSH server 9.1 allows remote attackers to crash an unauthenticated sshd child process via a crafted client banner. compat_kex_proposal() frees options.kex_algorithms when SSH_OLD_DHGEX matches, leaving a dangling pointer that kex_assemble_names() frees again during authentication setup. A default configuration accepts the trigger before authentication, but the fault occurs in a sandboxed, unprivileged child, and practical code execution requires defeating memory protections.

CVSS severity6.5
Medium
EPSS probability89.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in OpenSSH server 9.1 allows remote attackers to crash an unauthenticated sshd child process via a crafted client banner. compat_kex_proposal() frees options.kex_algorithms when SSH_OLD_DHGEX matches, leaving a dangling pointer that kex_assemble_names() frees again during authentication setup. A default configuration accepts the trigger before authentication, but the fault occurs in a sandboxed, unprivileged child, and practical code execution requires defeating memory protections.

The record

CVE
CVE-2023-25136
Published
Feb 3, 2023
Updated
May 28, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-415, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 3, 2023CVE publishedPublication date reported by the CVE source.
  2. May 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-415Double Free
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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