CVE-2024-8176: libexpat Stack Overflow DoS Vulnerability

CVE-2024-8176 Overview

CVE-2024-8176 is a stack overflow vulnerability in the libexpat XML parsing library. The flaw resides in how the library handles recursive entity expansion within XML documents. When libexpat parses a document containing deeply nested entity references, the parser recurses without bound, exhausting available stack space and crashing the host process. The defect is classified under CWE-674: Uncontrolled Recursion.

Because libexpat is embedded in countless operating systems, language runtimes, and applications, the blast radius for this issue is wide. Linux distributions including Red Hat Enterprise Linux, Ubuntu, Debian, Alpine, and SUSE shipped advisories, and NetApp also published downstream guidance.

Critical Impact
A network-reachable attacker can deliver a malicious XML document to any application linking libexpat and force a denial of service. In some environments the stack exhaustion may be coaxed into exploitable memory corruption.

Affected Products

libexpat versions prior to 2.7.0
Red Hat Enterprise Linux packages updated through advisories RHSA-2025:3531, RHSA-2025:3734, RHSA-2025:4048, and later errata
Downstream consumers including Debian, Ubuntu, Alpine Linux, SUSE, and NetApp products that bundle libexpat

Discovery Timeline

2025-03-14 - CVE-2024-8176 published to NVD
2025-03-15 - Issue announced on the OpenWall oss-security mailing list
2026-04-15 - Last updated in NVD database

Technical Details for CVE-2024-8176

Vulnerability Analysis

The defect lives in the entity expansion logic of libexpat, an event-driven XML parser written in C. XML allows documents to declare named entities that reference other entities. When the parser encounters a reference, it expands the target entity inline before continuing. libexpat implemented this expansion using direct recursion on the C call stack.

An attacker can craft a Document Type Definition (DTD) that chains entities so each references the next at increasing depth. Parsing such a document forces the library to recurse once per nesting level. With a sufficiently deep chain, the call stack overflows and the process aborts. The vulnerability is reachable any time libexpat accepts attacker-influenced XML, including SOAP endpoints, configuration parsers, document converters, and feed readers.

Root Cause

The root cause is uncontrolled recursion [CWE-674]. The entity processing path lacked a depth ceiling and relied on the operating system stack to bound recursion. Expat 2.7.0 reworks the affected code paths to perform iterative expansion and to enforce an explicit recursion limit, as described in the Expat 2.7.0 release notes and tracked in libexpat issue #893 with the fix landing through pull request #973.

Attack Vector

Exploitation requires no authentication or user interaction. An attacker submits a malicious XML payload to any service that invokes libexpat to parse untrusted input. Successful exploitation crashes the parsing process, producing denial of service. According to the advisory, the stack corruption may be turned into memory corruption in specific build configurations, which raises the upper bound of impact beyond availability.

No verified public exploit code is available. The vulnerability mechanism is documented in the libexpat change log for R_2_7_0 and the Red Hat CVE record.

Detection Methods for CVE-2024-8176

Indicators of Compromise

Repeated crashes, core dumps, or SIGSEGV signals in processes that consume XML, such as web servers, RPC daemons, document converters, and language runtimes that link libexpat.
XML payloads with hundreds or thousands of nested <!ENTITY> declarations or recursive entity references observed in proxy or WAF logs.
Sudden restarts or watchdog activity for services exposing SOAP, XML-RPC, or RSS endpoints.

Detection Strategies

Inventory installed libexpat versions across hosts using rpm -q expat, dpkg -l libexpat1, apk info expat, or equivalent and flag any version below 2.7.0.
Inspect application dependency manifests for statically bundled copies of expat that distro patches will not address.
Monitor inbound XML traffic for excessive entity declaration counts and abnormal nesting depth at the application gateway.

Monitoring Recommendations

Alert on process termination signals from XML-handling daemons and correlate with the inbound request that preceded the crash.
Track patch deployment progress against the relevant Red Hat, Ubuntu, Debian, SUSE, Alpine, and NetApp advisories listed in the references.
Subscribe to vendor security feeds for embedded products that have not yet published a fix, including third-party appliances that bundle libexpat.

How to Mitigate CVE-2024-8176

Immediate Actions Required

Upgrade libexpat to version 2.7.0 or later on every host, container image, and golden image in the environment.
Apply the corresponding distribution patch from the Red Hat advisories, Ubuntu USN, Debian tracker, Alpine commit, or NetApp advisory.
Rebuild and redeploy any in-house software that statically links or vendors libexpat sources.

Patch Information

The upstream fix ships in Expat 2.7.0. The release notes are published at the Hartwork blog, and the change log entry is available in the libexpat repository. Distribution backports are tracked under errata such as RHSA-2025:3531, RHSA-2025:3734, RHSA-2025:4048, RHSA-2025:4446, RHSA-2025:7444, RHSA-2025:8385, and the additional Red Hat advisories listed in the references. CERT/CC tracks the issue as VU#760160.

Workarounds

Reject XML documents that exceed a conservative entity nesting depth or entity declaration count at the network edge using a WAF or XML gateway.
Disable DTD processing in applications that do not require it, since the recursive expansion path requires entity declarations to be processed.
Run XML parsing services with strict resource limits, including reduced stack size via ulimit -s and process supervision that contains and restarts crashed workers until patches are applied.

bash

# Verify the installed libexpat version meets the fixed release
rpm -q expat        # Red Hat / Fedora
dpkg -l libexpat1   # Debian / Ubuntu
apk info -v expat   # Alpine

# Expected: expat >= 2.7.0