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6.3
CVE-2026-47270: pam_usb may misjudge remote login sessions
CVE-2026-47270 · published 5 months ago
Summary
The pam_usb module used for USB key logins on Linux can give the wrong answer about whether a login is coming from a remote computer. This happens when several login attempts happen at the same time, causing the module to mix up its data and make an incorrect decision. Updating pam_usb to version 0.9.0 resolves the issue.
Original advisory text
pam_usb: strtok() race condition in multi-threaded PAM hosts can corrupt deny_remote result
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.
References
- https://github.com/mcdope/pam_usb/security/advisories/GHSA-j3xw-vc43-x7jg Vendor Advisory
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47270... Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-47270 Vendor Advisory
- https://github.com/mcdope/pam_usb/commit/94f1640a61d49dfaf38e782680a52f01d5bf8b5... Patch
- https://github.com/mcdope/pam_usb/commit/d003e551b794a9e3774ff4720830fb7aadaa48b... Patch
Internet-facing
14 days
Internal
At next upgrade
- Not known to be exploited
- Needs hands-on effort to exploit
- Gives an attacker full control
Type
CWE-362Race Condition
Timeline
Published27 May 2026
Updated28 Oct 2026
First seen27 May 2026
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