CVE-2026-123158: flaw exploited in the wild, what we know

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.

• Severity: HIGH (CVSS 3.1 8.1, vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H).
• Weakness: CWE-394.
• NVD published 2026-11-05, status Received.

Anyone running CVE-2026-123158. Internet-facing instances are the priority.

NVD has not published affected version ranges for this CVE yet. Use the vendor advisory in the sources below to confirm which builds are affected.

• Exploited in the wild: added to the CISA Known Exploited Vulnerabilities catalog on 2026-11-09; federal remediation due date 2026-11-12.
• Public proof-of-concept code: 27 GitHub repositories from 27 accounts, the first on 2026-11-05.

CISA added CVE-2026-123158 to its Known Exploited Vulnerabilities catalog on 2026-11-09. A KEV listing means CISA has evidence that attackers are using the flaw against real systems, not just that it could be used.

If your business runs CVE-2026-123158, put this at the top of the patch list. CISA gave US federal agencies until 2026-11-12 to deal with it, and that is a sensible deadline for a small business too.

• Patch. Install the latest update from the vendor. NVD does not list a fixed version, so the vendor advisory linked on this page is the reference for which release closes it.
• If you cannot patch yet. Follow CISA's required action: 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 your exposure. Find out whether CVE-2026-123158 can be reached from the internet, for example a VPN portal, an admin login page or a file-transfer site. Your firewall's port-forwarding rules and your IT provider's list of public-facing systems are the quickest places to look. Exposed copies come first.
• When to call IT support. Call your IT support provider now if you run CVE-2026-123158 and cannot confirm it is updated, if it was reachable from the internet before you patched it, or if you notice accounts, sign-ins or files you do not recognise. The last two can mean the system was already hit, and checking that properly takes someone who can read the logs.

• EPSS (probability of exploitation activity in the next 30 days): 1.01%, higher than 63% of all scored CVEs (as of 2026-11-09).
• CVERadar threat level: 56/100 (see methodology).
• Likely ATT&CK techniques: T1078 Valid Accounts (inferred).

1. Find every instance. List where CVE-2026-123158 runs, including test, DR and forgotten internet-facing systems, and record the installed version.
2. Apply the latest vendor update. NVD does not list a fixed version, so follow the vendor advisory for the patched release.
3. If you can't patch today, follow CISA's required action: 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.
4. Verify the fix. Re-run the version check on every instance and confirm it reports the fixed build. Re-scan from outside if the service is exposed.
5. Hunt for signs of earlier compromise. If the system was exposed before you patched, assume it may have been hit and check the items below.
6. Rotate credentials stored on or used by the affected system if you cannot rule out compromise, and keep the logs you reviewed.

Detection hints

• T1078 Valid Accounts: Check for logins from new sources or accounts you did not create.

last -a | head -n 50
sudo grep -h "Accepted" /var/log/auth.log* /var/log/secure* 2>/dev/null | tail -n 50

Detection commands are generic starting points, not CVE-specific signatures. Use the indicators from the vendor advisory when it publishes them.

• NVD: CVE-2026-123158 nvd.nist.gov/vuln/detail/CVE-2026-123158
• CVE.org record www.cve.org/CVERecord?id=CVE-2026-123158
• Vendor link from CISA KEV www.openssh.org/releasenotes.html
• Vendor link from CISA KEV alpinelinux.org/posts/2026-11-05-openssh-password-authentication-bypas
• Vendor link from CISA KEV github.com/openssh/openssh-portable/commit/4353fdc43ef646c43a8dda7025c
• Vendor link from CISA KEV www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-up
• Vendor link from CISA KEV www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-
• CISA KEV catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (2026-11-09) api.first.org/data/v1/epss?cve=CVE-2026-123158