Vulnerability · Published May 27, 2026 · Assigned by GitHub_M

CVE-2026-48064pam_usb: PAM_RHOST check skipped when deny_remote=false allows XDMCP authentication bypass

High 8.1

In plain English

A high-severity incorrect authorization in pam_usb from mcdope. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 28% of all known vulnerabilities).

Severity (CVSS 3.1)8.1High

Exploit odds (30 days)0.3%top 72.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

pam_usb provides hardware authentication for Linux using ordinary removable media. Prior to 0.9.1, when a PAM service is configured with deny_remote=false in pam_usb (commonly done for display managers such as gdm-password or lightdm to bypass process/TTY heuristics for local sessions), the PAM_RHOST check in pusb_do_auth() is also skipped. PAM_RHOST is set by remote daemons (sshd, XDMCP servers) to identify the remote client address. Because the check is gated inside if (opts.deny_remote), a genuine remote XDMCP connection reaches the USB device authentication step instead of being rejected. This vulnerability is fixed in 0.9.1.

Affected products (as reported)

Vendor	Product	Versions
mcdope	pam_usb	< 0.9.1

Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

References

https://github.com/mcdope/pam_usb/security/advisories/GHSA-w38v-cw9r-x9p6 x_refsource_CONFIRM
https://github.com/mcdope/pam_usb/issues/348 x_refsource_MISC