Bug 2499232 (CVE-2026-52747)

Summary: CVE-2026-52747 ModSecurity: ModSecurity: Security rule bypass due to incorrect handling of line breaks in form data
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in ModSecurity, an open-source web application firewall (WAF). The multipart/form-data request body parser in libmodsecurity incorrectly handles embedded line breaks in non-file form-field values. This discrepancy between ModSecurity and backend applications, which preserve line breaks, can allow an attacker to bypass security rules. This bypass could lead to the execution of dangerous payloads that rely on line breaks, potentially resulting in a security compromise.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2499336, 2499335, 2499337, 2499338    
Bug Blocks:    

Description OSIDB Bzimport 2026-07-10 22:01:17 UTC 
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Prior to 3.0.16, the multipart/form-data request body parser in libmodsecurity silently removes embedded line breaks from non-file form-field values before exporting them to ARGS and ARGS_POST because src/request_body_processor/multipart.cc overwrites reserved bytes in m_reserve instead of appending the current buffer. This creates a parser differential between ModSecurity and backend applications that preserve line breaks in form fields, allowing rules that inspect ARGS or ARGS_POST to miss payloads whose dangerous syntax depends on a line break. This issue is fixed in version 3.0.16.