CVE-2026-47271
pam_usb: OOM guards removed by -DNDEBUG cause NULL dereference and authentication process crash
Description
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.
INFO
Published Date :
May 27, 2026, 8:16 p.m.
Last Modified :
May 27, 2026, 8:16 p.m.
Remotely Exploit :
No
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-47271
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update pam_usb to version 0.9.0 or later.
- Apply vendor patches if available for earlier versions.
- Monitor system for allocation failures during authentication.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-47271.
| URL | Resource |
|---|---|
| https://github.com/mcdope/pam_usb/commit/d003e551b794a9e3774ff4720830fb7aadaa48bd | |
| https://github.com/mcdope/pam_usb/security/advisories/GHSA-7rvx-jcc6-7hqq |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-47271 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-47271
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-47271 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-47271 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by [email protected]
May. 27, 2026
Action Type Old Value New Value Added Description 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. Added CVSS V3.1 AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-476 Added Reference https://github.com/mcdope/pam_usb/commit/d003e551b794a9e3774ff4720830fb7aadaa48bd Added Reference https://github.com/mcdope/pam_usb/security/advisories/GHSA-7rvx-jcc6-7hqq