CVE-2026-48981 pam_usb: xmlReadFile flags=0 permits XXE network entity fetching in conf.c
An XXE vulnerability in pam_usb allows attackers with config write access to trigger network requests or read local files during authentication.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-48981?
CVE-2026-48981 is a medium-severity vulnerability in mcdope pam_usb, published on 18 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
pam_usb provides hardware authentication for Linux using ordinary removable media. In versions prior to 0.9.2, pam_usb calls xmlReadFile() with flags=0 when loading the configuration file, allowing libxml2 to process external entity references (XXE), potentially making outbound network connections or local file reads at XML parse time from the context of the authenticating process. The vulnerability requires the configuration file to contain crafted XML entity references. Since pam_usb.conf is root-owned, direct exploitation requires prior write access to the config, but the defence-in-depth impact is significant given that pam_usb.so runs in setuid contexts (sudo, su). This issue has been fixed in version 0.9.2.
Weakness: CWE-611
Which versions are affected by CVE-2026-48981?
How do I fix CVE-2026-48981?
No fix has been published for CVE-2026-48981 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-48981 being exploited?
There is no known exploitation of CVE-2026-48981 in the wild and no public exploit code.
Sources
Also known as GHSA-96vv-r4wc-28c2.