CVE-2026-48983: CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition in mcdope pam_usb
pam_usb provides hardware authentication for Linux using ordinary removable media. In versions prior to 0.9.2, a symlink race condition exists in per-device and per-user pad directory creation. pam_usb uses a check-then-act pattern: it calls lstat() to test for existence and then calls mkdir() separately to create the directory. A local attacker can win the race between these calls by replacing the target path with a symlink to a directory they control. If successful, one-time pad files may be written to an attacker-controlled location, potentially exposing future pad values before use or disrupting authentication. This issue has been fixed in version 0.9.2.
AI Analysis
Technical Summary
The vulnerability in pam_usb (CVE-2026-48983) is a TOCTOU race condition affecting versions before 0.9.2. The software uses a check-then-act pattern where it calls lstat() to check if a directory exists and then calls mkdir() to create it. An attacker with local access can replace the directory path with a symlink after the check but before creation, causing one-time pad files to be written to an unintended location. This can lead to exposure of sensitive pad values or authentication disruption. The flaw is addressed in pam_usb version 0.9.2.
Potential Impact
A local attacker can exploit this race condition to redirect one-time pad files to attacker-controlled directories, potentially exposing sensitive cryptographic material used for authentication. This exposure can compromise confidentiality (high impact), cause integrity issues by disrupting authentication processes (low impact), and availability may also be affected (low impact).
Mitigation Recommendations
Upgrade pam_usb to version 0.9.2 or later, where this TOCTOU race condition has been fixed. No other mitigation or workaround is indicated.
CVE-2026-48983: CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition in mcdope pam_usb
Description
pam_usb provides hardware authentication for Linux using ordinary removable media. In versions prior to 0.9.2, a symlink race condition exists in per-device and per-user pad directory creation. pam_usb uses a check-then-act pattern: it calls lstat() to test for existence and then calls mkdir() separately to create the directory. A local attacker can win the race between these calls by replacing the target path with a symlink to a directory they control. If successful, one-time pad files may be written to an attacker-controlled location, potentially exposing future pad values before use or disrupting authentication. This issue has been fixed in version 0.9.2.
CVSS v3.1
Score 5.8medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in pam_usb (CVE-2026-48983) is a TOCTOU race condition affecting versions before 0.9.2. The software uses a check-then-act pattern where it calls lstat() to check if a directory exists and then calls mkdir() to create it. An attacker with local access can replace the directory path with a symlink after the check but before creation, causing one-time pad files to be written to an unintended location. This can lead to exposure of sensitive pad values or authentication disruption. The flaw is addressed in pam_usb version 0.9.2.
Potential Impact
A local attacker can exploit this race condition to redirect one-time pad files to attacker-controlled directories, potentially exposing sensitive cryptographic material used for authentication. This exposure can compromise confidentiality (high impact), cause integrity issues by disrupting authentication processes (low impact), and availability may also be affected (low impact).
Mitigation Recommendations
Upgrade pam_usb to version 0.9.2 or later, where this TOCTOU race condition has been fixed. No other mitigation or workaround is indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-26T23:26:07.975Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a344c3bf198dc38c1709d85
Added to database: 06/18/2026, 19:51:23 UTC
Last enriched: 06/25/2026, 21:18:41 UTC
Last updated: 08/01/2026, 19:18:00 UTC
Views: 105
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