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NULL Pointer DereferenceWeakness · CWE-476

CVE-2026-48985

MEDIUM · 5.5 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 →
57/100
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 0.9.1 and below, pusb_is_loginctl_local() can cause a NULL dereference crash when parsing loginctl output. The function calls popen() and reads the result; if the Remote field is only a newline, fgets() succeeds but strtok_r(buf, "\n", &saveptr) returns NULL. A subsequent strcmp(is_remote, "no") then dereferences NULL, causing undefined behavior (typically SIGSEGV) and crashing the PAM module. This can crash the authenticating process (e.g., sudo, login) and, depending on PAM stack configuration, deny access for all users of the affected service. 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 0.9.1 and below contain a NULL dereference vulnerability in the pusb_is_loginctl_local() function. When parsing loginctl output where the Remote field contains only a newline, fgets() succeeds but strtok_r() returns NULL. A subsequent strcmp() call then dereferences this NULL pointer, causing a SIGSEGV and crashing the PAM module.

MitigationUpgrade pam_usb to version 0.9.2 or later, which contains the fix for this NULL dereference vulnerability.

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
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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. Identify pam_usb installation and version
    Check for installed pam_usb package using your system package manager (e.g., dpkg -l | grep pam-usb, rpm -qa | grep pam-usb, or find /lib/security/ -name '*pam_usb*'). Compare the discovered version to the affected range: versions 0.9.1 and below.
    Affected if pam_usb is installed and its version is 0.9.1 or lower.
  2. Verify PAM module is enabled
    Examine PAM configuration files in /etc/pam.d/ for any entries referencing pam_usb.so (or pam_usb_auth.so). Also check /etc/pam.conf if used.
    Affected if A PAM configuration file references the pam_usb module, making the vulnerable code path reachable during authentication.
  3. Confirm loginctl is available and used
    Verify that the loginctl command exists on the system (which loginctl). The vulnerability triggers when pam_usb calls loginctl to check session locality.
    Affected if loginctl is present and pam_usb is configured to perform session checks, causing the vulnerable pusb_is_loginctl_local() function to be invoked.
  4. Check for specific Remote field condition
    Run loginctl to examine session output: loginctl [session-id] or loginctl list. Inspect the Remote field for sessions. The vulnerability triggers when Remote contains only a newline (appears empty or blank).
    Affected if Any active or recent PAM-authenticated session has a Remote field in loginctl output that contains only a newline character, which would cause strtok_r() to return NULL and trigger the crash.

A user is affected if pam_usb version 0.9.1 or lower is installed, the PAM module is enabled in an authentication configuration, and the vulnerable pusb_is_loginctl_local() function is invoked during loginctl output parsing where the Remote field contains only a newline.

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 contains the fix for this NULL dereference vulnerability.

Recommended fix High confidence

pam_usb version 0.9.2

  1. 1. Identify the current installed version of pam_usb using your package manager (e.g., dpkg -l pam-usb, rpm -qa | grep pam-usb, or check source version)
  2. 2. Upgrade pam_usb to version 0.9.2 or later using your system's package manager or by compiling from source
  3. 3. Verify the upgrade was successful by checking the installed version
  4. 4. Test the authentication functionality to confirm the vulnerability is mitigated

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

Have this fixed Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
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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-2026-48985 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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