Vulnerability in Alpine Linux configurations permits unauthorized SSH access

Researchers have identified a security vulnerability affecting devices running Alpine Linux, a distribution known for its lightweight footprint. The flaw arises from a specific interaction between the OpenSSH suite and the musl C library when Pluggable Authentication Modules (PAM) are disabled.

To exploit the vulnerability, attackers must target systems where user accounts are configured with a password hash using SHA256 or SHA512, and the account is marked as passwordless in the /etc/shadow file. This configuration is frequently employed for accounts utilizing certificate-based authentication, expanding the potential attack surface.

While Alpine Linux is the primary focus, other distributions utilizing this specific combination of OpenSSH, musl, and non-PAM authentication frameworks remain potentially at risk. The vulnerability, which has persisted for roughly a decade, allows for immediate, single-attempt access without requiring a password.