OpenBSD OpenSSH 9.1 compat.c options.kex_algorithms double free

CVSS Meta Temp Score
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CTI Interest Score
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5.9$5k-$25k0.00

Summaryinfo

A vulnerability has been found in OpenBSD OpenSSH 9.1 and classified as critical. The affected element is an unknown function of the file compat.c. Performing a manipulation of the argument options.kex_algorithms results in double free. This vulnerability was named CVE-2023-25136. The attack may be initiated remotely. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in OpenBSD OpenSSH 9.1 (Connectivity Software). It has been classified as critical. This affects an unknown part of the file compat.c. The manipulation of the argument options.kex_algorithms with an unknown input leads to a double free vulnerability. CWE is classifying the issue as CWE-415. The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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."

The weakness was presented 02/03/2023 as 486c4dc3b83b4b67d663fb0fa62bc24138ec3946. It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2023-25136 since 02/03/2023. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 05/29/2026).

The vulnerability scanner Nessus provides a plugin with the ID 242758 (NewStart CGSL MAIN 7.02 : openssh Multiple Vulnerabilities (NS-SA-2025-0124)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 9.2 eliminates this vulnerability. Applying the patch 486c4dc3b83b4b67d663fb0fa62bc24138ec3946 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (242758). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

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Version

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.0
VulDB Meta Temp Score: 5.9

VulDB Base Score: 5.6
VulDB Temp Score: 5.4
VulDB Vector: 🔍
VulDB Reliability: 🔍

NVD Base Score: 6.5
NVD Vector: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

Exploitinginfo

Class: Double free
CWE: CWE-415 / CWE-119
CAPEC: 🔍
ATT&CK: 🔍

Physical: No
Local: No
Remote: Yes

Availability: 🔍
Status: Not defined

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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Nessus ID: 242758
Nessus Name: NewStart CGSL MAIN 7.02 : openssh Multiple Vulnerabilities (NS-SA-2025-0124)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔍

Upgrade: OpenSSH 9.2
Patch: 486c4dc3b83b4b67d663fb0fa62bc24138ec3946

Timelineinfo

02/03/2023 🔍
02/03/2023 +0 days 🔍
02/03/2023 +0 days 🔍
05/29/2026 +1211 days 🔍

Sourcesinfo

Vendor: openbsd.org

Advisory: 486c4dc3b83b4b67d663fb0fa62bc24138ec3946
Status: Confirmed

CVE: CVE-2023-25136 (🔍)
GCVE (CVE): GCVE-0-2023-25136
GCVE (VulDB): GCVE-100-220083

Entryinfo

Created: 02/03/2023 08:25
Updated: 05/29/2026 13:32
Changes: 02/03/2023 08:25 (45), 02/03/2023 13:03 (3), 03/04/2023 10:52 (11), 07/26/2025 07:00 (17), 05/29/2026 13:32 (8)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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