CVE-2026-47272

pam_usb: OTP pad authentication bypass via missing system pad check and uninitialized RNG buffer

State: Published
Severity: 7.1 High
Published: May 27, 2026
Updated: May 28, 2026
Reserved: May 18, 2026

Description

pam_usb provides hardware authentication for Linux using ordinary removable media. Prior to 0.9.0, the pusb_pad_compare() function in src/pad.c only verified that the user-side pad (~/.pamusb/device.pad) could be read, but did not enforce that the system-side pad (the pad file on the USB device) was also present and readable. If the user-side pad was deleted or unreadable, the function returned a failure that was treated as non-fatal in certain code paths, allowing authentication to succeed without the USB device being verified. A local user can delete their own ~/.pamusb/device.pad to remove the USB device requirement and authenticate without the physical device. This vulnerability is fixed in 0.9.0.

Scores

CVSS	Score	Vector	Source
3.1	7.1 High	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N	GitHub_M

Weaknesses

CWE-287 Improper Authentication
CWE-908 Use of Uninitialized Resource

Affected Products

Product	Versions
pam_usbmcdope	< 0.9.0Affected

References

https://github.com/mcdope/pam_usb/security/advisories/GHSA-vx6f-rrqr-j87c

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