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 ARGSPOST because src/requestbodyprocessor/multipart.cc overwrites reserved bytes in mreserve 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 ARGSPOST to miss payloads whose dangerous syntax depends on a line break. This issue is fixed in version 3.0.16.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 through 3.0.15, the t:utf8toUnicode transformation in src/actions/transformations/utf8tounicode.cc produces wrong output on i386 architecture because snprintf uses sizeof on a char pointer rather than the length of the unicode buffer, allowing rules that use this transformation to be bypassed on i386 architecture. This issue is fixed in version 3.0.16.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 to before 3.0.15, there is an unhandled exception (std::outofrange) caused by unsigned integer underflow in libmodsecurity3 if the user (administrator) uses a rule any of @verifySSN, @verifyCPF, or @verifySVNR. This vulnerability is fixed in 3.0.15.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Hi,

On Sat, Apr 18, 2026 at 08:14:12AM -0400, cyber security wrote: Also you can use CVE-2026-33691, to disable security headers while bypassing CRS

More info at https://unlockoldupload.hashnode.dev/turn-off-security-headers-using-cve-2026-33691 This gives a 404 Page Not Found, but more importantly actual content should have been directly included in your posting, not only referenced via a link (although providing a link as well would then be OK). On Sat, Apr 18, 2026 at 3:00 AM cyber security <cs7778503 () gmail com> wrote: After deep analysis we confirm, that CVE-2026-33691 aka it alias UnlockOldUpload, can even disable ModSecurity WAF

More info at https://unlockoldupload.hashnode.dev/disable-modsecurity-waf-using-cve-2026-33691. This one exists. The gist of it is:

"upload a file called .htaccess with the content SecRuleEngine Off"

which should have been directly in your message.

With this, I think you've said enough about this CVE already, and should stop here - no further examples are needed.

Thanks,

Alexander

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. In versions 2.9.11 and below, an attacker can override the HTTP response’s Content-Type, which could lead to several issues depending on the HTTP scenario. For example, we have demonstrated the potential for XSS and arbitrary script source code disclosure in the latest version of modsecurity2. This issue is fixed in version 2.9.12.

ModSecurity is an open source intrusion detection and prevention engine for web applications.Security Fix(es): modsecurity: ModSecurity Denial of Service Vulnerability (CVE-2025-48866) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. In versions 2.9.8 to before 2.9.11, an empty XML tag can cause a segmentation fault. If SecParseXmlIntoArgs is set to On or OnlyArgs, and the request type is application/xml, and at least one XML tag is empty (eg <foo></foo>), then a segmentation fault occurs. This issue has been patched in version 2.9.11. A workaround involves setting SecParseXmlIntoArgs to Off.

ModSecurity is an open source intrusion detection and prevention engine for web applications.Security Fix(es): modsecurity: ModSecurity Has Possible DoS Vulnerability (CVE-2025-47947) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

ModSecurity is an open source intrusion detection and prevention engine for web applications.Security Fix(es): modsecurity: ModSecurity Has Possible DoS Vulnerability (CVE-2025-47947) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

ModSecurity is an open source intrusion detection and prevention engine for web applications.Security Fix(es): modsecurity: ModSecurity Has Possible DoS Vulnerability (CVE-2025-47947) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

ModSecurity is an open source intrusion detection and prevention engine for web applications.Security Fix(es): modsecurity: ModSecurity Has Possible DoS Vulnerability (CVE-2025-47947) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Versions prior to 2.9.10 contain a denial of service vulnerability similar to GHSA-859r-vvv8-rm8r/CVE-2025-47947. The sanitiseArg (and sanitizeArg - this is the same action but an alias) is vulnerable to adding an excessive number of arguments, thereby leading to denial of service. Version 2.9.10 fixes the issue. As a workaround, avoid using rules that contain the sanitiseArg (or sanitizeArg) action.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Versions prior to 2.9.10 contain a denial of service vulnerability similar to GHSA-859r-vvv8-rm8r/CVE-2025-47947. The sanitiseArg (and sanitizeArg - this is the same action but an alias) is vulnerable to adding an excessive number of arguments, thereby leading to denial of service. Version 2.9.10 fixes the issue. As a workaround, avoid using rules that contain the sanitiseArg (or sanitizeArg) action.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Versions up to and including 2.9.8 are vulnerable to denial of service in one special case (in stable released versions): when the payload's content type is application/json, and there is at least one rule which does a sanitiseMatchedBytes action. A patch is available at pull request 3389 and expected to be part of version 2.9.9. No known workarounds are available.

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Versions up to and including 2.9.8 are vulnerable to denial of service in one special case (in stable released versions): when the payload's content type is application/json, and there is at least one rule which does a sanitiseMatchedBytes action. A patch is available at pull request 3389 and expected to be part of version 2.9.9. No known workarounds are available.

Libmodsecurity is one component of the ModSecurity v3 project. The library codebase serves as an interface to ModSecurity Connectors taking in web traffic and applying traditional ModSecurity processing. A bug that exists only in Libmodsecurity3 version 3.0.13 means that, in 3.0.13, Libmodsecurity3 can't decode encoded HTML entities if they contains leading zeroes. Version 3.0.14 contains a fix. No known workarounds are available.

A buffer overflow in modsecurity v3.0.12 allows attackers to cause a Denial of Service (DoS) via a crafted input inserted into the name parameter. NOTE: this is disputed by the Supplier because it cannot be reproduced. Also, the product's documentation indicates that it is not guaranteed to be usable with very large values of SecRequestBodyNoFilesLimit (which are required by the claimed issue).

ModSecurity v3.0.x is affected by a Denial of Service vulnerability due to the global matching of regular expressions. The combination of a non-anchored regular expression and the ModSecurity “capture” action can be exploited via a specially crafted payload.

Known Affected Software Configurations:

ModSecurity v3.0.0 ModSecurity v3.0.1 ModSecurity v3.0.2 ModSecurity v3.0.3 ModSecurity v3.0.4 (patch for this version available

An issue was discovered in OWASP ModSecurity Core Rule Set (CRS) 3.0.2. Use of X.Filename instead of XFilename can bypass some PHP Script Uploads rules, because PHP automatically transforms dots into underscores in certain contexts where dots are invalid.

DISPUTED An issue was discovered in OWASP ModSecurity Core Rule Set (CRS) through 3.1.0. /rules/REQUEST-933-APPLICATION-ATTACK-PHP.conf allows remote attackers to cause a denial of service (ReDOS) by entering a specially crafted string with $a# at the beginning and nested repetition operators. NOTE: the software maintainer disputes that this is a vulnerability because the issue cannot be exploited via ModSecurity.

DISPUTED An issue was discovered in OWASP ModSecurity Core Rule Set (CRS) through 3.1.0. /rules/REQUEST-933-APPLICATION-ATTACK-PHP.conf allows remote attackers to cause a denial of service (ReDOS) by entering a specially crafted string with seterrorhandler# at the beginning and nested repetition operators. NOTE: the software maintainer disputes that this is a vulnerability because the issue cannot be exploited via ModSecurity.

DISPUTED An issue was discovered in OWASP ModSecurity Core Rule Set (CRS) through 3.1.0. /rules/REQUEST-933-APPLICATION-ATTACK-PHP.conf allows remote attackers to cause a denial of service (ReDOS) by entering a specially crafted string with next# at the beginning and nested repetition operators. NOTE: the software maintainer disputes that this is a vulnerability because the issue cannot be exploited via ModSecurity.

DISPUTED An issue was discovered in OWASP ModSecurity Core Rule Set (CRS) through 3.1.0. /rules/REQUEST-932-APPLICATION-ATTACK-RCE.conf allows remote attackers to cause a denial of service (ReDOS) by entering a specially crafted string with nested repetition operators. NOTE: the software maintainer disputes that this is a vulnerability because the issue cannot be exploited via ModSecurity.

An issue was discovered in OWASP ModSecurity Core Rule Set (CRS) through 3.1.0. /rules/REQUEST-942-APPLICATION-ATTACK-SQLI.conf allows remote attackers to cause a denial of service (ReDOS) by entering a specially crafted string with nested repetition operators.