pam_usb: TOCTOU race condition in pad directory creation allows symlink substitution

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Summary

CVECVE-2026-48983
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-18 20:16:14 UTC
Updated2026-06-22 17:56:35 UTC
Descriptionpam_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.

Risk And Classification

Primary CVSS: v3.1 5.8 MEDIUM from [email protected]

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

EPSS: 0.000840000 probability, percentile 0.003580000 (date 2026-06-25)

Problem Types: CWE-367 | CWE-367 CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.8MEDIUMCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L
3.1CNADECLARED5.8MEDIUMCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mcdope Pam Usb affected < 0.9.2 Not specified

References

ReferenceSourceLinkTags
github.com/mcdope/pam_usb/security/advisories/GHSA-4j8q-67fq-3xc3 [email protected] github.com
github.com/mcdope/pam_usb/releases/tag/0.9.2 [email protected] github.com
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