CVE-2004-2480: Squid Web Proxy Cache 2.3.STABLE5 allows remote attackers to bypass security controls and access arbitrary web

This month

MEDIUM 5.0DOWNGRADE

CVE-2004-2480 is a medium-severity flaw (CVSS 5.0) affecting squid web proxy cache. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Squid Web Proxy Cache 2.3.STABLE5 allows remote attackers to bypass security controls and access arbitrary websites via "@@" sequences in a URL within Internet Explorer.

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	3.0% (top 13%)
CISA exploited list	No
Published	2004-12-31
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

2004-12-31 05:00 UTCPublished CVE record published
2026-06-16 22:09 UTCUpdated Record last modified

national science foundation squid web proxy cache DOWNGRADE

Affected: 2.3_stable5

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.3_stable5

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.3_stable5 (Debian / Ubuntu)

apt-cache madison squid-web-proxy-cache sudo apt install squid-web-proxy-cache=<VERSION_BEFORE_2.3_stable5> sudo apt-mark hold squid-web-proxy-cache

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

dnf --showduplicates list squid-web-proxy-cache sudo dnf downgrade squid-web-proxy-cache-<VERSION_BEFORE_2.3_stable5> sudo dnf versionlock add squid-web-proxy-cache

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 Proxy 2.3 - Internet Access Control Bypass

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-2004-2480?

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

Is CVE-2004-2480 being exploited?

CVE-2004-2480 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-2004-2480 affect?

CVE-2004-2480 affects squid web proxy cache. Severity is medium (CVSS 5.0). Squid Web Proxy Cache 2.3.STABLE5 allows remote attackers to bypass security controls and access arbitrary websites via "@@" sequences in a URL within Internet Explorer.

How urgent is CVE-2004-2480?

Priority 44/100. Public exploit reference

Software pages

Internet Explorer vulnerabilities · Squid vulnerabilities

Related CVEs

CVE-2009-0801 MEDIUM 5.4 DOWNGRADE Squid, when transparent interception mode is enabled, uses the HTTP Host header to determine the remote endpoi
CVE-2007-6239 MEDIUM 5.0 DOWNGRADE The "cache update reply processing" functionality in Squid 2.x before 2.6.STABLE17 and Squid 3.0 allows remote
CVE-2004-2479 MEDIUM 5.0 DOWNGRADE Squid Web Proxy Cache 2.5 might allow remote attackers to obtain sensitive information via URLs containing inv
CVE-2004-0541 HIGH 10.0 DOWNGRADE Buffer overflow in the ntlm_check_auth (NTLM authentication) function for Squid Web Proxy Cache 2.5.x and 3.x,

References

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