CVE-2003-0899: Buffer overflow in defang in libhttpd.c for thttpd 2.21 to 2.23b1 allows remote attackers to execute arbitrary

Q: How urgent is CVE-2003-0899?

Priority 69/100. Critical severity; EPSS top 2%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2003-0899 is a critical-severity flaw (CVSS 9.8) affecting thttpd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Buffer overflow in defang in libhttpd.c for thttpd 2.21 to 2.23b1 allows remote attackers to execute arbitrary code via requests that contain '<' or '>' characters, which trigger the overflow when the characters are expanded to "<" and ">" sequences.

Why this priority

Critical severity
EPSS top 2%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	22.2% (top 2%)
CISA exploited list	No
Weakness	CWE-131
Published	2003-11-03
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: acme

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

Am I affected?

Timeline

2003-11-03 05:00 UTCPublished CVE record published
2026-06-16 22:03 UTCUpdated Record last modified

acme thttpd UPGRADE

Affected: >= 2.21 and < 2.23 · 2.23 · 2.23 b1

Fixed in: 2.23

Safe to downgrade to: a release before 2.21

1. Check installed version

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

2. UPGRADE to 2.23 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade thttpd

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade thttpd

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.21 (Debian / Ubuntu)

apt-cache madison thttpd sudo apt install thttpd=<VERSION_BEFORE_2.21> sudo apt-mark hold thttpd

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list thttpd sudo dnf downgrade thttpd-<VERSION_BEFORE_2.21> sudo dnf versionlock add thttpd

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: thttpd 2.2x - 'defang' Remote Buffer Overflow (PoC)
Exploit-DB: thttpd 2.2x - 'defang' Remote Buffer Overflow

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-2003-0899?

thttpd: upgrade to 2.23. Exact commands for each OS are on this page.

Is CVE-2003-0899 being exploited?

CVE-2003-0899 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-2003-0899 affect?

CVE-2003-0899 affects thttpd. Severity is critical (CVSS 9.8). Buffer overflow in defang in libhttpd.c for thttpd 2.21 to 2.23b1 allows remote attackers to execute arbitrary code via requests that contain '<' or '>' characters, which trigger the overflow when the characters are expanded to "<" and "

How urgent is CVE-2003-0899?

Priority 69/100. Critical severity; EPSS top 2%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

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References

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