CVE-2026-64669
pam_usb: deny_remote bypassed by compressed IPv6 addresses in pusb_tmux_has_remote_clients
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.
Fixes and workarounds
No remediation reported in collected sources.
Missing remediation information is not evidence that no patch exists.
Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| pam_usb mcdope |
>= 0.8.0, < 0.9.3 (affected) | CNA: GitHub_M |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 3.1 / 7.4 high |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N | CNA: GitHub_M |
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-2v34CNA: GitHub_M · x_refsource_CONFIRM
- https://github.com/mcdope/pam_usb/pull/423CNA: GitHub_M · x_refsource_MISC
- https://github.com/mcdope/pam_usb/commit/a62513f3da871d6576d751de3482eb80b9ac79f3CNA: GitHub_M · x_refsource_MISC
- https://github.com/mcdope/pam_usb/releases/tag/0.9.3CNA: GitHub_M · x_refsource_MISC
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