OpenSSH auth bypass flaw hits musl libc systems
OpenSSH sshd before 10.6p2 can let attackers bypass password authentication on musl libc Linux systems like Alpine running without PAM.
Sourceadvisories.ncsc.nl — open the original
What to check
- Applies to
- The 1 CVE named below. Whether you run an affected version is not assessed: check the versions the source lists.
- Exploitation
- CISA lists CVE-2026-123158 as exploited in the wild.
The OpenSSH Project patched a vulnerability affecting sshd versions prior to 10.6p2 that allows bypassing SSH password authentication under specific conditions. The flaw stems from an interaction between OpenSSH's authentication handling and musl libc's crypt() implementation on Linux systems that do not use PAM, such as Alpine Linux. Exploitation requires password lengths between 257 and 1024 bytes combined with a particular account configuration: the target system must use musl libc, run OpenSSH without PAM, have PasswordAuthentication enabled, and have at least one account with a '*' password hash alongside another account using a valid SHA-256 or SHA-512 hash. Standard glibc-based distributions such as Debian and Ubuntu are not affected.
While the CVSS score is 8.1, real-world exploitability is constrained to a narrow set of configurations, primarily musl-based distributions like Alpine Linux running SSH without PAM. NCSC-NL recommends not exposing SSH management services directly to the internet, restricting access to trusted networks, and disabling password authentication where not strictly necessary. No in-the-wild exploitation is reported; this is a vendor-patched vulnerability disclosure.
Defenders running Alpine Linux or other musl libc-based systems with OpenSSH configured without PAM should upgrade to OpenSSH 10.6p2 or later and review account configurations for the described password hash pattern as a precaution.
Mentioned in this report
Source reporting: https://advisories.ncsc.nl/2026/ncsc-2026-0469.html
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