CVE-2020-25580Network attack vector

Login authorization bypass via incorrect negative matching

Published Mar 26, 2021 · Updated Aug 4, 2024

Incorrect comparison in FreeBSD 11.4 and 12.2 allows remote authenticated users to bypass configured login denials through PAM. The login.access rule processor mishandles negative list entries, so a denial rule that should match is treated as nonmatching and pam_login_access returns success. Exploitation requires valid account credentials and a system that relies on custom login.access policy; successful attempts grant only the login access assigned to that account.

CVSS severity5.3
Medium
EPSS probability0.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect comparison in FreeBSD 11.4 and 12.2 allows remote authenticated users to bypass configured login denials through PAM. The login.access rule processor mishandles negative list entries, so a denial rule that should match is treated as nonmatching and pam_login_access returns success. Exploitation requires valid account credentials and a system that relies on custom login.access policy; successful attempts grant only the login access assigned to that account.

The record

CVE
CVE-2020-25580
Published
Mar 26, 2021
Updated
Aug 4, 2024
Vendor
The FreeBSD Project
Product
FreeBSD
Classifications
CWE-697, T1078
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=FreeBSD 12.2-RELEASE before p4, 11.4-RELEASE before p8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The FreeBSD Project · FreeBSDversion=FreeBSD 12.2-RELEASE before p4, 11.4-RELEASE before p8

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-697Incorrect Comparison
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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