CVE-2026-48981

In versions prior to 0.9.2, pam_usb has a symlink race condition in per-device and per-user pad directory creation. A local attacker can exploit this vulnerability by replacing the target path with a symlink to a directory they control.

In versions prior to 0.9.2, pam_usb creates a temporary file without the O_EXCL flag when updating a one-time pad file. This can lead to a situation where two concurrent processes updating the same pad may both succeed, resulting in overwriting the pad value.

In versions prior to 0.9.2, the pam_usb module, responsible for hardware authentication on Linux, is vulnerable to environment variable injection. The XRDP_SESSION, DISPLAY, and TMUX variables can be manipulated by a local user, affecting the local and remote session checking logic.

In pam_usb versions 0.9.1 and earlier, a bug can lead to an infinite loop DoS due to improper initialization of the *ppid variable. In the pusb_local_login() function, the same variable is reused as input and output in a loop, which can cause the authenticating process to hang.

In versions 0.9.1 and below, the pam_usb module can cause a NULL dereference crash when parsing loginctl output. The pusb_is_loginctl_local() function calls popen() and reads the result, which can lead to undefined behavior and crashing the PAM module.

In versions 0.9.1 and below, the xfree() function in pam_usb releases memory without first zeroing the buffer contents, leading to the exposure of sensitive data in freed memory. This could allow recovery of pad values or other authentication material from freed memory regions.

In pam_usb prior to 0.9.0, three functions used by the deny_remote feature called the non-reentrant strtok(), which stores state in a single global pointer. If two authentications race, one thread's strtok() call can overwrite the other's in-progress tokenisation pointer, causing incorrect parsing of tmux session data or the /proc environ scan. Additionally, pusb_tmux_get_client_tty() passed the raw pointer returned by getenv(TMUX) directly to strtok(), permanently corrupting the TMUX variable in the process. This vulnerability is fixed in 0.9.0.

In pam_usb before 0.9.0, the deny_remote feature checks utmpx ut_addr_v6 but only tests the first 32-bit word of the 128-bit address. IPv4-mapped IPv6 addresses (::ffff:x.x.x.x) have a zero first word, so IPv4 SSH sessions are incorrectly treated as local. This allows bypassing the deny_remote restriction and authenticating over SSH with a registered USB device.

In versions prior to 0.8.7, pam_usb reads the user's $TMUX environment variable and interpolates its value without proper sanitization, allowing arbitrary shell syntax injection. This creates a risk of unauthorized command execution as root.

pam_usb prior to version 0.8.7 allows remote code execution (RCE) as root through a crafted UUID in the configuration. Running pamusb-conf --reset-pads with such a UUID leads to exploitation of the vulnerability.