CVE-1999-1481: Squid 2.2.STABLE5 and below, when using external authentication, allows attackers to bypass access controls vi

This month

MEDIUM 5.0DOWNGRADE

CVE-1999-1481 is a medium-severity flaw (CVSS 5.0) affecting squid web proxy. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Squid 2.2.STABLE5 and below, when using external authentication, allows attackers to bypass access controls via a newline in the user/password pair.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.0 (Medium)
EPSS exploit chance	3.6% (top 11%)
CISA exploited list	No
Published	1999-12-31
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: national science foundation

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

1999-12-31 05:00 UTCPublished CVE record published
2026-06-16 21:50 UTCUpdated Record last modified

national science foundation squid web proxy DOWNGRADE

Affected: 1.0 · 1.0novm · 1.1 · 2.1 · 2.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

1. Check installed version

apt-cache policy squid-web-proxy || rpm -q squid-web-proxy || squid-web-proxy --version

2. No fixed release: DOWNGRADE to a release before 1.0 (Debian / Ubuntu)

apt-cache madison squid-web-proxy sudo apt install squid-web-proxy=<VERSION_BEFORE_1.0> sudo apt-mark hold squid-web-proxy

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list squid-web-proxy sudo dnf downgrade squid-web-proxy-<VERSION_BEFORE_1.0> sudo dnf versionlock add squid-web-proxy

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: National Science Foundation Squid Web Proxy 1.0/1.1/2.1 - Authentication Failure

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-1999-1481?

squid web proxy: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-1999-1481 being exploited?

CVE-1999-1481 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-1999-1481 affect?

CVE-1999-1481 affects squid web proxy. Severity is medium (CVSS 5.0). Squid 2.2.STABLE5 and below, when using external authentication, allows attackers to bypass access controls via a newline in the user/password pair.

How urgent is CVE-1999-1481?

Priority 45/100. Public exploit reference

Software pages

Squid vulnerabilities

Related CVEs

CVE-2001-1030 HIGH 7.5 DOWNGRADE DOWNGRADE Squid before 2.3STABLE5 in HTTP accelerator mode does not enable access control lists (ACLs) when the httpd_ac
CVE-2001-0843 MEDIUM 5.0 UPGRADE Squid proxy server 2.4 and earlier allows remote attackers to cause a denial of service (crash) via a mkdir-on
CVE-2001-0142 LOW 1.2 DOWNGRADE DOWNGRADE squid 2.3 and earlier allows local users to overwrite arbitrary files via a symlink attack in some configurati

References

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