---
id: CVE-2026-104269
title: >-
  ModSecurity: RFC 2231 `filename*` Parameter Bypasses Multipart Filename Rules
  on RFC-Compliant Backends (Go, Python, Node, Java)
summary: >-
  ModSecurity is an open source, cross platform web application firewall (WAF)
  engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, ModSecurity's
  multipart parser does not apply the RFC 2231 filename* parameter precedence
  used by com…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N'
cvssSource: cna
cwe:
  - CWE-436
vendor: owasp-modsecurity
product: ModSecurity
affected:
  - 'ModSecurity >= 3.0.0, < 3.0.17'
published: '2026-11-05'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T15:51:18.332Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-104269'
references:
  - url: >-
      https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-5pww-8rfg-9crf
    label: >-
      https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-5pww-8rfg-9crf
  - url: >-
      https://github.com/owasp-modsecurity/ModSecurity/commit/463db0c840fa27bfba095b0406a63004a12884b0
    label: >-
      https://github.com/owasp-modsecurity/ModSecurity/commit/463db0c840fa27bfba095b0406a63004a12884b0
  - url: >-
      https://github.com/owasp-modsecurity/ModSecurity/commit/c6bd53d2dd96766b3afdc35d9929ebb20925d13d
    label: >-
      https://github.com/owasp-modsecurity/ModSecurity/commit/c6bd53d2dd96766b3afdc35d9929ebb20925d13d
  - url: 'https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v2.9.15'
    label: 'https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v2.9.15'
  - url: 'https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17'
    label: 'https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17'
tags:
  - cve.org
ingestedAt: '2026-11-05T21:36:00.926Z'
---

## Overview

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, ModSecurity's multipart parser does not apply the RFC 2231 filename* parameter precedence used by common Go, Python, Node.js, and Java application parsers. A Content-Disposition header can provide a benign filename parameter for ModSecurity and a different encoded filename* value that the backend prefers, causing MULTIPART_FILENAME rules and the application to make security decisions on different names. Applications that use the backend-selected name for storage, extension checks, or content-type inference can therefore receive a filename that bypassed WAF inspection. PHP's native multipart parser is not affected by this discrepancy. This issue is fixed in version 3.0.17.

## Affected

- `ModSecurity >= 3.0.0, < 3.0.17`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.