mcdope pam_usb up to 0.8.x on Linux PAM Module src/mem.c xmalloc null pointer dereference

Summaryinfo

A vulnerability classified as problematic was found in mcdope pam_usb up to 0.8.x on Linux. Affected by this vulnerability is the function xmalloc of the file src/mem.c of the component PAM Module. Executing a manipulation can lead to null pointer dereference. This vulnerability is registered as CVE-2026-47271. The attack needs to be launched locally. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability has been found in mcdope pam_usb up to 0.8.x on Linux and classified as problematic. This vulnerability affects the function xmalloc of the file src/mem.c of the component PAM Module. The manipulation with an unknown input leads to a null pointer dereference vulnerability. The CWE definition for the vulnerability is CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. As an impact it is known to affect availability. CVE summarizes:

pam_usb provides hardware authentication for Linux using ordinary removable media. Prior to 0.9.0, src/mem.c implemented out-of-memory guards for xmalloc(), xrealloc(), and xstrdup() using assert(data != NULL). The C standard specifies that all assert() expressions are compiled out when NDEBUG is defined at build time. NDEBUG is commonly defined in release and packaging builds (Debian, Fedora, Arch package flags all define it via -DNDEBUG in CFLAGS). With the guard removed, xmalloc/xrealloc/xstrdup silently return NULL on allocation failure. Every caller in the codebase dereferences the return value without a NULL check -- this is the intended design, as the guard was supposed to abort before the dereference. With the guard gone, any allocation failure causes a NULL pointer dereference, crashing the PAM module. A crash in a PAM module loaded by sudo or login causes authentication to fail for the duration of the crash, creating a local denial-of-service condition. An attacker who can induce memory pressure at authentication time can lock all users out of sudo and login. This vulnerability is fixed in 0.9.0.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-47271 since 05/19/2026. The exploitation appears to be difficult. The attack needs to be approached locally. There are known technical details, but no exploit is available.

Upgrading to version 0.9.0 eliminates this vulnerability. Applying the patch d003e551b794a9e3774ff4720830fb7aadaa48bd is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• mcdope

Name

• pam_usb

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8

License

• open-source

Website

• Product: https://github.com/mcdope/pam_usb/

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