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CVE-2026-48986: pam_usb: Infinite loop DoS in process-tree walk when parent process exits during authentication

• Severity: medium (CVSS 4.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-18 · updated 2026-10-26
• Weakness: CWE-835

Description

pam_usb provides hardware authentication for Linux using removable media. In pam_usb 0.9.1 and earlier, usb_get_process_parent_id() can cause an infinite loop DoS because it does not initialize *ppid on failure. In pusb_local_login(), the same variable is reused as input and output in a process-tree while loop; if /proc/<pid>/stat cannot be read (for example, when an ancestor process exits during authentication), the PID is not updated and the loop does not terminate. This hangs the authenticating process (such as sudo, sshd, or login) until it is forcibly terminated. This issue has been fixed in version 0.9.2.

Affected products

• mcdope pam_usb: before 0.9.2

References

• https://github.com/mcdope/pam_usb/releases/tag/0.9.2
• https://github.com/mcdope/pam_usb/security/advisories/GHSA-h28h-9hc3-v595

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