{"id":"CVE-2026-47270","aliases":["EUVD-2026-32655","GHSA-j3xw-vc43-x7jg"],"status":"published","title":"pam_usb: strtok() race condition in multi-threaded PAM hosts can corrupt deny_remote result","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.","severity":{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00108,"percentile":0.01182,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-362"],"published":"2026-05-27T20:10:37Z","modified":"2026-10-28T11:11:16Z","products":[{"vendor":"mcdope","product":"pam_usb"}],"references":[{"url":"https://github.com/mcdope/pam_usb/security/advisories/GHSA-j3xw-vc43-x7jg","tags":["x_refsource_CONFIRM","advisory"]},{"url":"https://github.com/mcdope/pam_usb/commit/94f1640a61d49dfaf38e782680a52f01d5bf8b51","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/mcdope/pam_usb/commit/d003e551b794a9e3774ff4720830fb7aadaa48bd","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47270.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47270","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-47270","title":"pam_usb: strtok() race condition in multi-threaded PAM hosts can corrupt deny_remote result","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.","status":"published","published":"2026-05-27T20:10:37.108Z","modified":"2026-05-28T13:25:31.065Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-362"],"updated_at":"2026-11-02T13:36:40.478484Z"}],"euvd":[{"id":"EUVD-2026-32655","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.","status":"published","published":"2026-05-27T20:10:37Z","modified":"2026-05-28T13:25:31Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N","level":"medium"}],"updated_at":"2026-11-02T18:21:03.0662Z"}],"nvd":[{"id":"CVE-2026-47270","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.","status":"published","published":"2026-05-27T21:16:18.95Z","modified":"2026-10-26T12:10:00.13Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-362"],"updated_at":"2026-11-02T14:12:20.885865Z"}],"osv":[{"id":"CVE-2026-47270","title":"pam_usb: strtok() race condition in multi-threaded PAM hosts can corrupt deny_remote result","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.","status":"published","published":"2026-05-27T20:10:37.108Z","modified":"2026-10-28T11:11:16.654053256Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N","level":"medium"}],"cwes":["CWE-362"],"updated_at":"2026-11-02T15:45:06.231145Z"}]}}