CVE-2026-73857: ModSecurity v3 XML Request Body Processor Uninitialized Pointer Dereference Vulnerability
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.15 until 3.0.17, XML request body processing with SecParseXmlIntoArgs set to On or OnlyArgs can leave XMLNodes::parsingctxarg uninitialized in the SAX end-element callback. A single crafted unauthenticated HTTP request can make a worker dereference the pointer, resulting in a constant-value write to an attacker-controlled address. The resulting memory corruption can terminate the worker and may disclose memory or redirect execution. Earlier 3.0.x releases and ModSecurity 2.x do not use the affected path. This issue is fixed in version 3.0.17.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
ModSecurityto a version that resolves this vulnerability.Fixed in 3.0.17
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
The affected path is used by ModSecurity v3 deployments that process XML request bodies with SecParseXmlIntoArgs set to On or OnlyArgs. Earlier 3.0.x releases and ModSecurity 2.x do not use this path.
Does exploitation require authentication or interaction from a user?
No. A remote attacker can send a single crafted unauthenticated HTTP request to trigger the vulnerable XML processing path.
What is the operational impact and available fix?
Successful exploitation can corrupt memory, terminate a worker, and may disclose memory or redirect execution. The issue is fixed in ModSecurity version 3.0.17.