CVE-2026-52747 describes a vulnerability in ModSecurity's multipart/form-data parser before version 3.0.16. The parser incorrectly removes embedded line breaks from non-file form-field values due to overwriting reserved bytes instead of appending the current buffer. This leads to a parser differential between ModSecurity and backend applications that preserve line breaks, causing security rules that inspect ARGS or ARGS_POST to miss payloads relying on line breaks for dangerous syntax. The vulnerability is classified under CWE-180 (Incorrect Behavior Order: Validate Before Canonicalize).

This vulnerability can allow attackers to bypass security rules in ModSecurity that inspect form field arguments (ARGS and ARGS_POST) because the WAF removes line breaks that backend applications preserve. As a result, payloads that depend on line breaks for their malicious syntax may evade detection, potentially leading to successful injection or other attacks. The CVSS score is 8.6 (high severity), indicating a significant risk of impact on integrity without requiring privileges or user interaction.

This issue is fixed in ModSecurity version 3.0.16. Users should upgrade to version 3.0.16 or later to remediate this vulnerability. No official patch or temporary fix is indicated other than upgrading. Since this is not a cloud service, remediation depends on user action to update the software.