Executive Summary

CVE-2026-48986 is a medium-severity vulnerability in the pam_usb software, affecting versions 0.9.1 and earlier. It involves an infinite loop denial-of-service (DoS) condition during the authentication process.

The flaw occurs in the function usb_get_process_parent_id() when it fails to initialize the ppid variable upon failure. This causes a process-tree walk loop in pusb_local_login() to never terminate if an ancestor process exits during authentication, because the PID is not updated.

As a result, the authenticating process (such as sudo, sshd, or login) hangs indefinitely until it is forcibly terminated.

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Mitigation Strategies

The immediate mitigation step is to upgrade pam_usb to version 0.9.2 or later, where the issue has been fixed by initializing the parent process ID variable to prevent the infinite loop.

Until the upgrade can be applied, monitor authentication processes for hangs and forcibly terminate any stuck processes to maintain system availability.

Additionally, consider limiting the use of pam_usb on busy systems where short-lived processes frequently appear in the ancestor chain of authentication calls.

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Impact Analysis

This vulnerability can cause the authentication process on a Linux system using pam_usb to hang indefinitely, resulting in a denial-of-service condition.

Specifically, processes like sudo, sshd, or login may become unresponsive, requiring manual termination.

On busy systems where short-lived processes frequently appear in the ancestor chain, this issue is more likely to be triggered.

The overall impact is a disruption of availability, potentially affecting system access and operations.

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Detection Guidance

This vulnerability causes an infinite loop denial-of-service (DoS) condition during authentication processes such as sudo, sshd, or login, resulting in those processes hanging until forcibly terminated.

To detect this vulnerability on your system, monitor for authentication processes that become unresponsive or hang unexpectedly.

You can use commands to identify hung authentication processes, for example:

• Use `ps` to find stuck authentication processes: `ps -eo pid,ppid,cmd | grep -E 'sudo|sshd|login'` and look for processes with unusually long runtimes.
• Use `strace` on suspected hung processes to observe if they are stuck in a loop: `strace -p <pid>`.
• Check system logs (e.g., `/var/log/auth.log` or `/var/log/secure`) for repeated authentication attempts or errors related to PAM or usb authentication.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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