Bug 2567712 (CVE-2026-104269)

Summary:	CVE-2026-104269 modsecurity: mod_security: ModSecurity: Security inspection bypass via multipart filename parameter discrepancy
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	csutherl, jclere, pjindal, plodge, rhel-process-autobot, szappis, vchlup, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in ModSecurity. The multipart parser fails to properly prioritize parameter handling when processing filenames in Content-Disposition headers. A remote attacker can exploit this discrepancy by submitting a request containing both a benign filename and an encoded alternative that the backend application prefers. This allows an attacker to bypass Web Application Firewall (WAF) inspection rules, enabling uninspected or malicious files to reach the backend application.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
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Description OSIDB Bzimport 2026-11-05 22:20:01 UTC

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.