# CVE-2026-64669: pam_usb: deny_remote bypassed by compressed IPv6 addresses in pusb_tmux_has_remote_clients

Status: published. Published: 2026-11-11. Updated: 2026-11-11.

pam_usb provides hardware authentication for Linux using removable media. From version 0.8.0 to before version 0.9.3, the deny_remote feature in pam_usb uses /usr/bin/w -i to detect whether the authenticating user has an active remote tmux session. In pusb_tmux_has_remote_clients() (src/tmux.c), the IPv6 detection regex required exactly four explicit colon-separated groups of 1-4 hex digits (e.g. 2001:0db8:85a3:0000). Any IPv6 address in compressed notation — including loopback (::1), link-local (fe80::1), and global unicast addresses (2001:db8::1) — did not match this pattern. As a result the remote-client check silently returned "no remote clients" even when a remote tmux client was connected from such an address. This issue has been patched in version 0.9.3.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- mcdope / pam_usb: >= 0.8.0, < 0.9.3 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 7.4 (high); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-285, CWE-693

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/mcdope/pam_usb/pull/423 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/mcdope/pam_usb/commit/a62513f3da871d6576d751de3482eb80b9ac79f3 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/mcdope/pam_usb/releases/tag/0.9.3 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-64669; retrieved 2026-11-11; source updated 2026-11-11

Revision: cdc73d01b4b8e184e0a0e16bb79aa6c000c53efacb7e0a030ea936c1ee32f305

Canonical: https://y2.dev/cve/CVE-2026-64669

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