# CVE-2026-47270: pam_usb: strtok() race condition in multi-threaded PAM hosts can corrupt deny_remote result

> A race condition in pam_usb's remote session detection can allow attackers to bypass hardware authentication restrictions on Linux systems.

- **Severity:** Medium 6.3 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 May 2026
- **Updated:** 28 May 2026
- **Also known as:** GHSA-j3xw-vc43-x7jg

## What is CVE-2026-47270?

CVE-2026-47270 is a medium-severity vulnerability in mcdope pam_usb, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

pam_usb provides hardware authentication for Linux using ordinary removable media. Prior to 0.9.0, pam_usb is a PAM module loaded into the host process (sudo, login, GDM, GNOME Shell). Display managers such as GDM run multiple concurrent authentication threads. Three functions used by the deny_remote feature called the non-reentrant strtok(), which stores state in a single global pointer. If two authentications race, one thread's strtok() call can overwrite the other's in-progress tokenisation pointer, causing incorrect parsing of the tmux session data or the /proc environ scan that backs the remote-session detection logic. Additionally, pusb_tmux_get_client_tty() passed the raw pointer returned by getenv(TMUX) directly to strtok(). getenv() returns a pointer into the live process environment block; strtok() inserts NUL bytes into that block, permanently corrupting the TMUX variable for subsequent code running in the same process. In long-lived display managers this affects all future authentications in that process. The combined effect can cause deny_remote=true to return an incorrect decision for a remote session, or an incorrect decision for a local session, depending on thread interleaving. This vulnerability is fixed in 0.9.0.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-47270?


## How do I fix CVE-2026-47270?

No fix has been published for CVE-2026-47270 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-47270 being exploited?

There is no known exploitation of CVE-2026-47270 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-47270 and fix it if it is affected.

What it is: CVE-2026-47270 is a medium-severity vulnerability in mcdope pam_usb, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-47270 in the wild and no public exploit code.

Affected product: mcdope pam_usb. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-47270/ (Markdown: https://insights.sbomify.com/CVE-2026-47270/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-47270
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-47270
- OSV: https://osv.dev/vulnerability/CVE-2026-47270

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-47270/
Summaries are generated and may contain mistakes; the official description above is the record.