CVE-2006-6303: The read_multipart function in cgi.rb in Ruby before 1.8.5-p2 does not properly detect boundaries in MIME mult

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MEDIUM 5.0DOWNGRADE

CVE-2006-6303 is a medium-severity flaw (CVSS 5.0) affecting ruby. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The read_multipart function in cgi.rb in Ruby before 1.8.5-p2 does not properly detect boundaries in MIME multipart content, which allows remote attackers to cause a denial of service (infinite loop) via crafted HTTP requests, a different issue than CVE-2006-5467.

Why this priority

EPSS top 10%: very likely to be exploited

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

Risk facts

CVSS score	5.0 (Medium)
EPSS exploit chance	3.8% (top 10%)
CISA exploited list	No
Weakness	CWE-399
Published	2006-12-06
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: yukihiro matsumoto

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

Am I affected?

Timeline

2006-12-06 19:28 UTCPublished CVE record published
2026-06-16 22:32 UTCUpdated Record last modified

yukihiro matsumoto ruby DOWNGRADE

Affected: 1.8 · 1.8.1 · 1.8.2 · 1.8.2_pre1 · 1.8.2_pre2 · 1.8.3 · 1.8.4 · 1.8.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.8

1. Check installed version

apt-cache policy ruby || rpm -q ruby || ruby --version

2. No fixed release: DOWNGRADE to a release before 1.8 (Debian / Ubuntu)

apt-cache madison ruby sudo apt install ruby=<VERSION_BEFORE_1.8> sudo apt-mark hold ruby

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

dnf --showduplicates list ruby sudo dnf downgrade ruby-<VERSION_BEFORE_1.8> sudo dnf versionlock add ruby

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-2006-6303?

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

Is CVE-2006-6303 being exploited?

CVE-2006-6303 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-2006-6303 affect?

CVE-2006-6303 affects ruby. Severity is medium (CVSS 5.0). The read_multipart function in cgi.rb in Ruby before 1.8.5-p2 does not properly detect boundaries in MIME multipart content, which allows remote attackers to cause a denial of service (infinite loop) via crafted HTTP requests, a different i

How urgent is CVE-2006-6303?

Priority 40/100. EPSS top 10%: very likely to be exploited

Software pages

Ruby vulnerabilities

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References

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