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Linux PamApplication

CVE-2020-27780

CRITICAL · 9.8 CVSS v3.1 Published 2020-12-18
Fix available
A fix is available. Upgrade to 1.5.1 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges 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
A flaw was found in Linux-Pam in versions prior to 1.5.1 in the way it handle empty passwords for non-existing users. When the user doesn't exist PAM try to authenticate with root and in the case of an empty password it successfully authenticate.

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

A privilege escalation and authentication bypass vulnerability in Linux-PAM versions prior to 1.5.1 allows authentication with root privileges when PAM attempts to authenticate a non-existent user with an empty password. The module incorrectly falls back to root authentication and accepts an empty password, bypassing all normal authentication controls.

MitigationUpgrade Linux-PAM to version 1.5.1 or later. Before upgrading, restrict direct root login access and ensure alternative authentication mechanisms are available in case of issues.

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

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux PamApplication
Affected:>= 1.5.0, < 1.5.1

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 Linux-PAM version
    Run 'rpm -q pam' (RHEL/CentOS) or 'dpkg -l libpam0g' (Debian/Ubuntu) or 'pacman -Q pam' (Arch) to retrieve the installed PAM package version
    Affected if The installed version is 1.5.0 or falls between 1.5.0 and 1.5.1 (e.g., 1.5.0-1, 1.5.0-2)
  2. Locate PAM password authentication configuration
    Examine /etc/pam.d/system-auth or /etc/pam.d/common-auth (path varies by distribution) for password authentication module configurations
    Affected if PAM is configured to use pam_unix.so or pam_unix2.so for password authentication and the configuration is active
  3. Verify password authentication stack order
    Review the PAM configuration files to confirm the order of authentication modules, particularly looking for pam_unix.so referenced in password or auth sections
    Affected if The pam_unix module is present in the authentication stack and handles password verification
  4. Test authentication with non-existent user
    Attempt to authenticate using a system tool (such as 'su' or 'login') with a non-existent username and an empty password; observe whether access is granted
    Affected if Authentication succeeds with root privileges when providing a non-existent username and empty password

You are affected if Linux-PAM version 1.5.0 is installed and PAM authentication is configured to use the vulnerable module, allowing empty password authentication for non-existent users.

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
Upgrade available Upgrade to 1.5.1 or later
Fixed in 1.5.1
Interim mitigation

Upgrade Linux-PAM to version 1.5.1 or later. Before upgrading, restrict direct root login access and ensure alternative authentication mechanisms are available in case of issues.

Recommended fix Moderate confidence

1.5.1

  1. Obtain Linux-PAM version 1.5.1 from your distribution's official package repository
  2. Backup the current PAM configuration files (/etc/pam.d/*) before upgrading
  3. Upgrade the pam package using your system's package manager
  4. Verify the new version is 1.5.1 or later
  5. Test authentication functionality to ensure PAM is working correctly
  6. Restart any services that rely on PAM authentication if needed
Caveat Upgrading PAM can affect system authentication; ensure you have console/physical access in case of issues

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

Fix this in Linux Pam Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2020-27780 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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