CVE-2009-3720

What it is

The updatePosition function in lib/xmltok_impl.c in libexpat in Expat 2.0.1, as used in Python, PyXML, w3c-libwww, and other software, allows context-dependent attackers to cause a denial of service (application crash) via an XML document with crafted UTF-8 sequences that trigger a buffer over-read, a different vulnerability than CVE-2009-2625.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

27.9% chance of exploitation in the next 30 days (EPSS). Higher than most.

Fix

No patch or advisory is linked yet. Look at mitigations or restrict exposure.

Timeline

1. 2009-11-03 16:30 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-07-20 14:35 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 27.9% in the next 30 days (EPSS).
• Severity: 5.0 MEDIUM (CVSS).
• Fix: none linked yet, which raises it.

Details

Published

2009-11-03 16:30 UTC

Last modified

2026-07-20 14:35 UTC

Exploit probability

27.9% · EPSS, next 30 days

Record status

Modified

Affected

• Libexpat Project Libexpat 2.0.1
• Apache Http Server < 2.0.64
• Apache Http Server < 2.2.17

Attack profile CVSS 2.0 · 5.0

Attack vector

Network

Complexity

Low

Authentication

None

Confidentiality

None

Integrity

None

Availability

Partial

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2009-3720.md and follow it. Check whether this project is affected by CVE-2009-3720. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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