VU#760160: libexpat library is vulnerable to DoS attacks through stack overflow

Overview

A stack overflow vulnerability has been discovered within the libexpat open source library. When parsing XML documents with deeply nested entity references, libexpat can recurse indefinitely. This can result in exhaustion of stack space and a crash. An attacker can weaponize this to either perform denial of service (DoS) attacks or memory corruption attacks, based on the libexpat environment and library usage.

Description

libexpat is an Open Source XML parsing library. It is a stream oriented XML parsing library written in the C programming language. It can be used in particular with large files difficult for processing in RAM. A vulnerability has been discovered, tracked as CVE-2024-8176. The vulnerability description can be observed below.

CVE-2024-8176

A stack overflow vulnerability exists in the libexpat library due to the way it handles recursive entity expansion in XML documents. When parsing an XML document with deeply nested entity references, libexpat can be forced to recurse indefinitely, exhausting the stack space and causing a crash. This issue could lead to denial of service (DoS) or, in some cases, exploitable memory corruption, depending on the environment and library usage.

Impact

An attacker with access to software that uses libexpat could provide a XML document to the program and cause a DoS attack or memory corruption attack. libexpat is used in a variety of different software, and by various companies.

Solution

A patch for the vulnerability has been provided in version 2.7.0 of libexpat. Groups that use libexpat can verify their patch using the POCs provided here: https://github.com/libexpat/libexpat/issues/893#payload_generators

Acknowledgements

This vulnerability was reported to us by the maintainer of the project, Sebastian Pipping, to increase awareness. The vulnerability was originally discovered by Jann Horn of Googles Project Zero. Vendors who wish to join the discussion within VINCE can do so here: https://www.kb.cert.org/vince/. This document was written by Christopher Cullen.