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Actively exploited

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.

From the CISA KEV catalogue version 2026.11.10, with Cybergen analysis. Updated 10 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 9 Nov 2026.
  • Rated High severity (CVSS 8.1, scored by Vendor).
The Vulnerability

What It Is

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.

Affected Versions

ProductVersions
OpenBSD OpenSSHbefore 10.6p2

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for OpenBSD OpenSSH. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    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.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated high, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies have until 12 Nov 2026 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited OpenBSD Flaws

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

All 2 exploited OpenBSD vulnerabilities

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2026-123158
  3. CVE record: CVE-2026-123158
  4. FIRST EPSS
  5. alpinelinux.org/posts/2026-11-05-openssh-password-authentication-bypass/
  6. github.com/openssh/openssh-portable/commit/4353fdc43ef646c43a8dda7025cc1a898caf1482
  7. openssh.org/releasenotes.html#10.6p2
  8. news.ycombinator.com/item?id=50377976
  9. news.ycombinator.com/item?id=50378228
  10. marc.info/?l=openssh-unix-dev&m=179388064263131&w=2
  11. hachyderm.io/@damienmiller/117563026759098135
  12. github.com/predkambrij/sshhole-repro