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Exploited vulnerability · CISA KEV

Is CVE-2026-123158 exploited? Yes: in CISA KEV since 9 Nov 2026

Gociux · OpenBSD OpenSSH · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2026-123158, OpenBSD OpenSSH Unexpected Status Code or Return Value Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 9 Nov 2026, 4 days after it was published. It affects OpenBSD OpenSSH. If you run it, CISA's required action is: 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.

exploitedYesCISA KEV · 9 Nov 2026
ransomwareNot knownno confirmed use
EPSStop 5%very likely to be exploited
severity8.1CVSS 3.1 · high
US federal due12 Nov 2026BOD 22-01 deadline

What it is

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

VendorOpenBSD (2 exploited CVEs in KEV)
ProductOpenSSH
VulnerabilityOpenBSD OpenSSH Unexpected Status Code or Return Value Vulnerability
WeaknessCWE-394
Published5 Nov 2026
Added to KEV9 Nov 2026
Reported by (CNA)mitre

What to do

  1. Check whether you run it. Look for OpenSSH in your asset inventory, including appliances and cloud images. Stack check lists every exploited OpenBSD CVE at once.
  2. Apply the fix. 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.
  3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 5 Nov 2026.
  4. Get told next time. Email alerts when CISA adds a CVE for OpenBSD.

References

Questions

Is CVE-2026-123158 being exploited?

Yes. CISA added CVE-2026-123158 to the Known Exploited Vulnerabilities catalog on 9 Nov 2026, which means there is reliable evidence of exploitation in the wild.

Is CVE-2026-123158 used in ransomware attacks?

CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.

How do I fix CVE-2026-123158?

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. Check OpenBSD's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected OpenSSH and watch it for signs of compromise.

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2026 · OpenBSD scorecard · act-now radar.

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