Known exploited vulnerability · CISA KEV

CVE-2026-123158: OpenBSD OpenSSH Unexpected Status Code or Return Value Vulnerability

OpenBSD OpenSSH on Linux contains an unexpected status code or return value vulnerability that could allow for authentication bypass.

CVE-2026-123158

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2026-11-09: attackers are using it right now.

CISA KEV: Listed; Added 2026-11-09 · federal fix-by 2026-11-12
EPSS (30 days): 1.0%; Higher than 63% of CVEs · 2026-11-09
CVSS v3.1: 8.1 High; CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

What CISA says

OpenBSD OpenSSH Unexpected Status Code or Return Value Vulnerability

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

NVD description · published 2026-11-05

sshd in OpenSSH before 10.6p2 on Linux, when musl libc is used without PAM, lacks a workaround for a password authentication bypass (related to misinterpretation of whether a string is intended to be a password hash). For some configurations of accounts, any password between 256 and 1024 characters succeeds. An example of a platform using musl libc without PAM is Alpine Linux.

Full record on NVD

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How to check if you are exposed to CVE-2026-123158

Find every OpenBSD OpenSSH system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2026-123158.

US federal agencies had to fix this by 2026-11-12. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Timeline

2026-11-05 · Published in the National Vulnerability Database
2026-11-09 · Added to CISA's Known Exploited Vulnerabilities catalog, 4 days after it was published
2026-11-12 · Fix-by date for US federal agencies, still ahead

Vendor advisories and fixes

Weakness type

CWE-394

More exploited OpenBSD vulnerabilities

CISA lists 2 exploited OpenBSD vulnerabilities. The closest matches:

CVE-2020-7247OpenSMTPD Remote Code Execution VulnerabilityAdded 2022-03-25

Keep going

Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.11.09); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-09. This product uses the NVD API but is not endorsed or certified by the NVD.