CVE-2026-64669: pam_usb auth bypass in deny

Q: Is CVE-2026-64669 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Q: What does this mean?

With deny_remote enabled, pam_usb is meant to block access when the user has a remote tmux session. A flaw in how compressed IPv6 addresses are checked can hide that remote session, so access is granted as if no remote session existed.

Q: Which versions are affected by CVE-2026-64669?

pam_usb: from 0.8.0 before 0.9.3.

Q: Am I affected, and how do I check?

pam_usb versions 0.8.0 up to and including 0.9.2 are in the affected range, and the issue only applies when deny_remote is enabled and the session comes from a compressed IPv6 address. To check, look at the installed pam_usb version and whether deny_remote is set in the pam_usb configuration.

Q: How do I fix CVE-2026-64669?

Upgrade pam_usb to 0.9.3, which is the fixed version listed for this range.

Summary

pam_usb, a Linux hardware authentication tool that uses removable media, fails to detect remote tmux clients connected from IPv6 addresses written in compressed form, so its deny_remote protection can be bypassed by an attacker who can reach the system over the network without logging in. The check wrongly reports no remote clients when such a connection exists, which lets authentication proceed despite the remote session.

Read the original 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 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.

Who should check

Anyone running mcdope pam_usb 0.8.0 through 0.9.2 with deny_remote enabled on hosts that allow remote tmux sessions

Read the source excerpt

“>= 0.8.0, <= 0.9.2”

github.com

cve.now Index

24Pcve.now Index 24 of 100 · methodology v3 · provisional

Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
Reach?/20Unknown. No tracked technology or package matched
Severity7.4/10CVSS 7.4
No patch0/5No signal

What would change the score

Would score about 69 if added to CISA KEV
Would score about 64 if CISA's SSVC rates exploitation active
Would score about 29 if advisories confirm default setups are exposed

How the score works · Rankings

What to do

Upgrade to a fixed version: 0.9.3.

Check your systems with an agent

Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.

Check whether my systems are affected by CVE-2026-64669 (pam_usb: deny_remote bypassed by compressed IPv6 addresses in pusb_tmux_has_remote_clients), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-64669 (entry last updated 2026-11-11):
Affected:
- mcdope pam_usb: from 0.8.0, fixed in 0.9.3
Fixed versions: 0.9.3.
Conditions (all must be true for the bug to be hit):
- pam_usb versions from 0.8.0 up to and including 0.9.2 (source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34)
- The deny_remote feature is enabled and the target user has a remote tmux session, using a compressed IPv6 address (source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-64669 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-64669 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34
- https://github.com/mcdope/pam_usb/pull/423
- https://github.com/mcdope/pam_usb/commit/a62513f3da871d6576d751de3482eb80b9ac79f3
- https://github.com/mcdope/pam_usb/releases/tag/0.9.3
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Entry: https://cve.now/CVE-2026-64669
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-64669.

Timeline

Nov 11, 2026, 3:52 AM UTCCVE published
Nov 11, 2026, 4:01 AM UTCFirst seen by cve.now

Affected versions

mcdope pam_usb
From 0.8.0 · fixed in 0.9.3

Evidence 6

Vendor advisory · 1

Establishes: Affected and fixed versions.

Advisory
GitHub · mcdope/pam_usb · Advisory GHSA-gc4c-v52c-2v34

CVE record · 2

Establishes: The identifier and description.

Record
CVE List · CVE-2026-64669
Record
NVD · CVE-2026-64669

Corrections

None so far.

Something wrong on this page? Report an error. Every fix is listed here.

Questions about CVE-2026-64669

Is CVE-2026-64669 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data

What does this mean?

With deny_remote enabled, pam_usb is meant to block access when the user has a remote tmux session. A flaw in how compressed IPv6 addresses are checked can hide that remote session, so access is granted as if no remote session existed.Source: github.com

Which versions are affected by CVE-2026-64669?

pam_usb: from 0.8.0 before 0.9.3.Source: cve.now feed data

Am I affected, and how do I check?

pam_usb versions 0.8.0 up to and including 0.9.2 are in the affected range, and the issue only applies when deny_remote is enabled and the session comes from a compressed IPv6 address. To check, look at the installed pam_usb version and whether deny_remote is set in the pam_usb configuration.Source: github.com

How do I fix CVE-2026-64669?

Upgrade pam_usb to 0.9.3, which is the fixed version listed for this range.Source: github.com

pam_usb: deny_remote bypassed by compressed IPv6 addresses in pusb_tmux_has_remote_clients