CVE-2024-8176: 
Bottlerocket vulnerability analysis and mitigation

CVE-2024-8176 is a stack overflow vulnerability discovered in the libexpat library, reported in March 2025. The vulnerability exists due to the way libexpat 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 (Ubuntu Security, MITRE CVE).

The vulnerability has three distinct variants or 'faces': general entities in character data, general entities in attribute values, and parameter entities. The issue can be triggered by supplying a specially crafted XML document designed to create a long chain of recursive entities, essentially functioning as a 'linear version of billion laughs' attack. The vulnerability has received a CVSS 3.1 Base Score of 7.5 (High) with a vector of CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (Hartwork Blog).

The primary impact is denial of service (DoS), with the potential for exploitable memory corruption depending on the environment and library usage. The attack can be made more efficient when XML input is combined with compression, which can significantly reduce the minimum attack payload size (Hartwork Blog).

The vulnerability is reliably exploitable for denial of service attacks. The required chain length for exploitation depends on the stack size of the target machine, with approximately 23,000 levels of nesting being sufficient on some systems. The attack can be executed through three different methods: general entities in character data, general entities in attribute values, and parameter entities (Hartwork Blog).

The vulnerability has been fixed in libexpat version 2.7.0. The fix involves resolving the use of recursion for all three variants of entity usage. Organizations are strongly advised to upgrade to this version. The fix was developed through a collaborative effort involving multiple companies including Siemens and Red Hat (Hartwork Blog).

The vulnerability was initially reported by Jann Horn of Google Project Zero in July 2022, and the fix was developed over approximately 10 months through collaboration between multiple organizations including Siemens, Linutronix, and Red Hat. The security community has emphasized the broader lesson about the dangers of recursion in C software, with the maintainer stating 'Please leave recursion to math and keep it out of (in particular C) software: it kills and will kill again' (Hartwork Blog).