CVE-2009-3720
MediumExploitation Probability (EPSS)
Very high risk98th percentile - higher than 98% of all known CVEs
Summary
The updatePosition function in libexpat (Expat 2.0.1) has a buffer over-read vulnerability. Crafted UTF-8 sequences in an XML document can cause an application crash.
Risk Assessment
An attacker can remotely cause a denial of service (DoS) by sending a malicious XML document to an application using the vulnerable Expat version, potentially disrupting system operations.
Recommendation
Update the Expat library to version 2.0.2 or later, and update all dependent software (Python, PyXML, w3c-libwww).
Other vulnerabilities in Expat
See all- CVE-2016-4472High
The overflow protection in Expat is removed by compilers with certain optimization settings, allowing remote attackers to cause a denial of service (crash) or possibly execute arbitrary code via crafted XML data.
- CVE-2016-0718Critical
Expat allows context-dependent attackers to cause a denial of service (crash) or possibly execute arbitrary code via a malformed input document, which triggers a buffer overflow.
- CVE-2026-76641High
Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for CVE-2026-66046.
- CVE-2026-66046High
Denial of service vulnerability in Expat through 2.8.3. The storeAtts() function in xmlparse.c has quadratic complexity, causing excessive CPU consumption when processing an XML document with many attributes with non-normalized values.
Original NVD description (English source)
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.