CVE-2026-64668: Access Control Flaw (CVSS 7.4)

Description

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.

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CVSS v3.1 Score

7.4

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0038

Probability of exploitation

0.33%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-285 CWE-285

CWE-693 CWE-693

References

Other References

https://github.com/mcdope/pam_usb/commit/a62513f3da871d6576d751de3482eb80b9ac79f3 https://github.com/mcdope/pam_usb/pull/423 https://github.com/mcdope/pam_usb/releases/tag/0.9.3 https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf

Frequently Asked Questions

What is CVE-2026-64668? +

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. It has a CVSS v3.1 base score of 7.4 (HIGH).

How severe is CVE-2026-64668? +

CVE-2026-64668 has a CVSS v3.1 score of 7.4 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0038, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-64668? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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