CVE-2026-52747: CWE-180: Incorrect Behavior Order: Validate Before Canonicalize in owasp-modsecurity ModSecurity
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.
AI Analysis
Technical Summary
CVE-2026-52747 affects ModSecurity, an open source web application firewall engine. The multipart/form-data parser in versions before 3.0.16 incorrectly removes embedded line breaks from non-file form-field values due to overwriting reserved bytes instead of appending buffers. This leads to a parser differential between ModSecurity and backend applications, allowing certain payloads that rely on line breaks to evade detection by security rules inspecting ARGS or ARGS_POST. The vulnerability is classified under CWE-180 (Incorrect Behavior Order: Validate Before Canonicalize) and has a CVSS 3.1 score of 8.6 (high severity). The issue is resolved in ModSecurity version 3.0.16.
Potential Impact
This vulnerability can cause ModSecurity to miss malicious payloads in multipart/form-data requests if those payloads depend on embedded line breaks for their dangerous syntax. As a result, attackers may bypass security rules that inspect ARGS or ARGS_POST, potentially leading to successful exploitation of web applications protected by vulnerable ModSecurity versions. The vulnerability does not impact confidentiality or availability but has a high impact on integrity due to the potential for undetected injection or manipulation attacks.
Mitigation Recommendations
Upgrade ModSecurity to version 3.0.16 or later, where this issue is fixed. There is no indication of alternative mitigations or temporary workarounds. Patch status is confirmed fixed in 3.0.16.
CVE-2026-52747: CWE-180: Incorrect Behavior Order: Validate Before Canonicalize in owasp-modsecurity ModSecurity
Description
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.
CVSS v3.1
Score 8.6high
Affected software
pkg:github/owasp-modsecurity/ModSecurityRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-52747 affects ModSecurity, an open source web application firewall engine. The multipart/form-data parser in versions before 3.0.16 incorrectly removes embedded line breaks from non-file form-field values due to overwriting reserved bytes instead of appending buffers. This leads to a parser differential between ModSecurity and backend applications, allowing certain payloads that rely on line breaks to evade detection by security rules inspecting ARGS or ARGS_POST. The vulnerability is classified under CWE-180 (Incorrect Behavior Order: Validate Before Canonicalize) and has a CVSS 3.1 score of 8.6 (high severity). The issue is resolved in ModSecurity version 3.0.16.
Potential Impact
This vulnerability can cause ModSecurity to miss malicious payloads in multipart/form-data requests if those payloads depend on embedded line breaks for their dangerous syntax. As a result, attackers may bypass security rules that inspect ARGS or ARGS_POST, potentially leading to successful exploitation of web applications protected by vulnerable ModSecurity versions. The vulnerability does not impact confidentiality or availability but has a high impact on integrity due to the potential for undetected injection or manipulation attacks.
Mitigation Recommendations
Upgrade ModSecurity to version 3.0.16 or later, where this issue is fixed. There is no indication of alternative mitigations or temporary workarounds. Patch status is confirmed fixed in 3.0.16.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-08T14:00:43.573Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a516c2c68715ace434381f3
Added to database: 07/10/2026, 22:03:24 UTC
Last enriched: 07/18/2026, 15:32:34 UTC
Last updated: 08/24/2026, 22:52:12 UTC
Views: 85
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