CVE-2026-48066
Deferred Deferred - Pending Action

Race Condition in pam_usb Authentication Module

Publication date: 2026-05-27

Last updated on: 2026-05-27

Assigner: GitHub, Inc.

Description
pam_usb provides hardware authentication for Linux using ordinary removable media. Prior to 0.9.1, src/log.c contains a process-wide static pointer that is written on every PAM invocation with the address of a stack-local variable. This violates the PAM re-entrancy requirement and creates a data race when the PAM stack is invoked concurrently from multiple threads. This vulnerability is fixed in 0.9.1.

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Meta Information

Published
2026-05-27
Last Modified
2026-05-27
Generated
2026-07-07
AI Q&A
2026-05-27
EPSS Evaluated
2026-07-05
NVD
CVE-2026-48066

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
mcdope pam_usb to 0.9.1 (exc)
mcdope pam_usb From 0.9.1 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-362 The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
CWE-476 The product dereferences a pointer that it expects to be valid but is NULL.

Attack-Flow Graph

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Impact Analysis

This vulnerability can lead to data races during concurrent PAM invocations, potentially causing unexpected behavior or crashes in the authentication process. The CVSS score indicates a moderate impact with a high impact on availability, meaning it could disrupt authentication services but does not directly compromise confidentiality.

Mitigation Strategies

To mitigate this vulnerability, upgrade pam_usb to version 0.9.1 or later, where the issue has been fixed.

Compliance Impact

The provided information does not specify any direct impact of the CVE-2026-48066 vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

Detection Guidance

The vulnerability can be detected by checking for data races during concurrent PAM authentication invocations involving pam_usb versions 0.9.0 and earlier.

One suggested method is to build pam_usb with ThreadSanitizer enabled using the compiler flag -fsanitize=thread.

Then, run concurrent invocations of the pamusb-check command to trigger the race condition and observe if ThreadSanitizer reports any data races.

  • Compile pam_usb with ThreadSanitizer: gcc -fsanitize=thread -o pamusb-check src/log.c other_sources.c
  • Run multiple concurrent pamusb-check commands, for example: for i in {1..10}; do ./pamusb-check & done; wait

If data races are detected, ThreadSanitizer will output warnings indicating the presence of the vulnerability.

Executive Summary

The vulnerability exists in pam_usb versions prior to 0.9.1, specifically in the src/log.c file. It involves a process-wide static pointer that is overwritten on every PAM invocation with the address of a stack-local variable. This design violates the PAM re-entrancy requirement and causes a data race when multiple threads invoke the PAM stack concurrently.

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