CVE-2009-0801: Squid, when transparent interception mode is enabled, uses the HTTP Host header to determine the remote endpoi

This month

MEDIUM 5.4DOWNGRADE

CVE-2009-0801 is a medium-severity flaw (CVSS 5.4) affecting squid web proxy cache. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Squid, when transparent interception mode is enabled, uses the HTTP Host header to determine the remote endpoint, which allows remote attackers to bypass access controls for Flash, Java, Silverlight, and probably other technologies, and possibly communicate with restricted intranet sites, via a crafted web page that causes a client to send HTTP requests with a modified Host header.

Why this priority

No elevated risk signals yet

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

Risk facts

CVSS score	5.4 (Medium)
EPSS exploit chance	3.1% (top 12%)
CISA exploited list	No
Weakness	CWE-264
Published	2009-03-04
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: squid

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

Am I affected?

Timeline

2009-03-04 16:30 UTCPublished CVE record published
2026-06-16 23:05 UTCUpdated Record last modified

squid squid web proxy cache DOWNGRADE

Affected: 2.7 · 2.7.stable5 · 2.7.stable6 · 3.0 · 3.0_pre1 · 3.0_pre2 · 3.0_pre3 · 3.0_stable1

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.7

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 2.7 (Debian / Ubuntu)

apt-cache madison squid-web-proxy-cache sudo apt install squid-web-proxy-cache=<VERSION_BEFORE_2.7> 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_2.7> 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.

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-2009-0801?

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

Is CVE-2009-0801 being exploited?

CVE-2009-0801 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-2009-0801 affect?

CVE-2009-0801 affects squid web proxy cache. Severity is medium (CVSS 5.4). Squid, when transparent interception mode is enabled, uses the HTTP Host header to determine the remote endpoint, which allows remote attackers to bypass access controls for Flash, Java, Silverlight, and probably other technologies, and pos

How urgent is CVE-2009-0801?

Priority 41/100. No elevated risk signals yet.

Software pages

Java vulnerabilities · Squid vulnerabilities

References

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