CVE-2026-47269 pam_usb: deny_remote feature incorrectly classifies IPv4-mapped IPv6 remote connections as local
Attackers with physical USB access can bypass remote authentication restrictions on Linux systems using pam_usb with specific IPv6 configurations.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-47269?
CVE-2026-47269 is a high-severity authentication bypass vulnerability in mcdope pam_usb, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-284
Which versions are affected by CVE-2026-47269?
How do I fix CVE-2026-47269?
No fix has been published for CVE-2026-47269 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-47269 being exploited?
There is no known exploitation of CVE-2026-47269 in the wild and no public exploit code.
Sources
Also known as GHSA-jmmj-qhrq-w45g.