mcdope pam_usb up to 0.8.x on Linux Removable Media deny_remote access control

Summaryinfo

A vulnerability categorized as critical has been discovered in mcdope pam_usb up to 0.8.x on Linux. This vulnerability affects the function deny_remote of the component Removable Media Handler. Executing a manipulation can lead to access control. This vulnerability is handled as CVE-2026-47269. The attack can be executed remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability has been found in mcdope pam_usb up to 0.8.x on Linux and classified as critical. This vulnerability affects the function deny_remote of the component Removable Media Handler. The manipulation with an unknown input leads to a access control vulnerability. The CWE definition for the vulnerability is CWE-284. The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

pam_usb provides hardware authentication for Linux using ordinary removable media. Prior to 0.9.0, pam_usb's deny_remote feature checks utmpx ut_addr_v6 to detect whether an authentication request originates from a remote session. The outer guard was if (utent->ut_addr_v6[0] != 0), which only tests the first 32-bit word of the 128-bit address field. IPv4-mapped IPv6 addresses (::ffff:x.x.x.x) store the IPv4 address in ut_addr_v6[3] with ut_addr_v6[0] == 0. On systems where the SSH daemon listens on :: (IPv6 wildcard) with AddressFamily any -- common on Ubuntu and Debian -- incoming IPv4 connections are recorded in utmpx as IPv4-mapped IPv6 addresses. The outer check evaluates to false, the remote-detection block is skipped entirely, and the session is treated as local. deny_remote=true does not block the authentication. An attacker with physical access to a registered USB device can authenticate over SSH on an affected system as if they were sitting at a local terminal, bypassing the deny_remote restriction. This vulnerability is fixed in 0.9.0.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-47269 since 05/19/2026. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1068.

Upgrading to version 0.9.0 eliminates this vulnerability. Applying the patch 804fe24eae3d742d8be05fd015e36abc3c7d94e5 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• mcdope

Name

• pam_usb

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8

License

• open-source

Website

• Product: https://github.com/mcdope/pam_usb/

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