pam_usb: OOM guards removed by -DNDEBUG cause NULL dereference and authentication process crash

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Summary

CVECVE-2026-47271
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-27 20:16:39 UTC
Updated2026-05-28 13:57:25 UTC
Descriptionpam_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.

Risk And Classification

Primary CVSS: v3.1 5.1 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-476 | CWE-476 CWE-476: NULL Pointer Dereference

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.1MEDIUMCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED5.1MEDIUMCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mcdope Pam Usb affected < 0.9.0 Not specified

References

ReferenceSourceLinkTags
github.com/mcdope/pam_usb/commit/d003e551b794a9e3774ff4720830fb7aadaa48bd [email protected] github.com
github.com/mcdope/pam_usb/security/advisories/GHSA-7rvx-jcc6-7hqq [email protected] github.com
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