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XML External Entity (XXE)Weakness · CWE-611

CVE-2026-48981

MEDIUM · 6.7 CVSS v3.1 Published 2026-06-18
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
69/100
Remediation priority · Elevated
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

pam_usb versions before 0.9.2 call xmlReadFile() with flags=0 when parsing pam_usb.conf, enabling XML External Entity (XXE) processing. This allows the authenticating process (running in setuid contexts like sudo/su) to make outbound network connections or read local files at XML parse time if the config contains crafted entity references. Exploitation requires prior write access to the root-owned config file.

MitigationUpgrade pam_usb to version 0.9.2 or later which implements secure XML parsing flags. If upgrade is not immediately possible, ensure the configuration file has restrictive permissions and monitor for unauthorized modifications.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
High
Privileges
High
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
Low

CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:L/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check if pam_usb is installed
    Look for pam_usb binary, library, or configuration files on the system. Common paths include /usr/lib/security/pam_usb.so, /usr/bin/pam_usb*, or check package manager output (dpkg -l | grep pam_usb, rpm -qa | grep pam-usb, or pacman -Q pam_usb)
    Affected if pam_usb package or binary is found on the system
  2. Determine installed pam_usb version
    Run the version command for pam_usb if available (pam_usb --version), or query the package manager (dpkg -s pam_usb, rpm -qi pam_usb, or pacman -Q pam_usb) to obtain the exact version number
    Affected if Version is present and less than 0.9.2
  3. Locate pam_usb.conf configuration file
    Search for pam_usb.conf - common locations are /etc/pam_usb.conf, /etc/security/pam_usb.conf, or check the pam_usb documentation for the configured path
    Affected if Configuration file exists and is readable by the checking user
  4. Verify XML parsing vulnerability exists
    If source code is available, inspect the source file that calls xmlReadFile() to confirm flags=0 is used. Otherwise, rely on version comparison since this flag setting was present in all versions before 0.9.2
    Affected if Installed version is below 0.9.2 and the configuration file is writable by an attacker (prior to exploitation)

User is affected if pam_usb version is below 0.9.2 and the pam_usb.conf configuration file exists on the system.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade pam_usb to version 0.9.2 or later which implements secure XML parsing flags. If upgrade is not immediately possible, ensure the configuration file has restrictive permissions and monitor for unauthorized modifications.

Recommended fix High confidence

pam_usb version 0.9.2

  1. 1. Check the current installed version of pam_usb by running 'pam_usb --version' or checking your package manager
  2. 2. Upgrade pam_usb to version 0.9.2 or later using your distribution's package manager (e.g., apt-get update && apt-get install pam-usb, yum update pam-usb, or dnf update pam-usb)
  3. 3. If upgrading from source, download version 0.9.2 or later from the official pam_usb repository and rebuild/install
  4. 4. Verify the installed version is 0.9.2 or higher using 'pam_usb --version'

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing4.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,540
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-48981 in production — separate from our analysis above.

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What this is

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