CVE-2026-64668: high-severity vulnerability in mcdope pam_usb
pam_usb: deny_remote bypassed by zone-indexed IPv6 addresses (fe80::1%eth0) in pusb_tmux_has_remote_clients
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.4epss 0.4%
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 pattern matched the address group and then immediately expected whitespace. On Linux systems with multi-homed network interfaces, w -i appends a zone index (scope identifier) to link-local IPv6 addresses — e.g. fe80::1%eth0. The %eth0 suffix appeared between the address and the next whitespace field, causing the regex match to fail even for an otherwise-matching remote session. The function returned "no remote clients" and granted access. This issue has been patched in version 0.9.3.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Affected products
mcdope · pam_usbRelated CVEs — mcdope pam_usb
In the same product, most dangerous first.
CVE-2026-64669HIGHpam_usb: deny_remote bypassed by compressed IPv6 addresses in pusb_tmux_has_remote_clientsEPSS 0.4%CVE-2026-48064HIGHpam_usb: PAM_RHOST check skipped when deny_remote=false allows XDMCP authentication bypassEPSS 0.3%CVE-2026-47269HIGHpam_usb: deny_remote feature incorrectly classifies IPv4-mapped IPv6 remote connections as localEPSS 0.3%CVE-2026-47273MEDIUMpam_usb: XPath injection via PAM-supplied identifiers in pam_usb configuration queriesEPSS 0.3%CVE-2026-44711HIGHpam_usb: Symlink attacks on pad directory and pad files enable authentication bypass and root file corruptionEPSS 0.2%CVE-2026-64666HIGHpam_usb: getenv() in pusb_local_login bypasses XRDP deny via env-var unsetEPSS 0.2%