CVE-2026-107835 in Coraza
Summary
by MITRE • 10/09/2026
OWASP Coraza WAF is a golang modsecurity compatible web application firewall library. Prior to 3.8.1, internal/cookies.ParseCookies in internal/cookies/cookies.go handles boundary ASCII control characters and control-only or empty cookie names differently from several backend cookie parsers. An unauthenticated attacker can craft a Cookie header so Coraza indexes or drops a cookie under a different name or value from the backend application, causing rules targeting REQUEST_COOKIES or REQUEST_COOKIES_NAMES to miss application-visible attacker data. Exploitation depends on the backend parser and affected rule scope, and interior control characters with inconsistent backend behavior are outside this advisory's remediation. This issue is fixed in version 3.8.1.
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Analysis
by VulDB Data Team • 10/09/2026
The vulnerability identified within OWASP Coraza WAF prior to version 3.8.1 represents a critical inconsistency in how the Web Application Firewall processes HTTP Cookie headers compared to backend application servers. As a Go-based library designed for ModSecurity compatibility, Coraza serves as an intermediary security layer that inspects incoming traffic before it reaches the protected web application. The core technical flaw resides in the internal/cookies.ParseCookies function located within the cookies.go module. This component is responsible for parsing and normalizing cookie data from HTTP requests to ensure that subsequent security rules can accurately evaluate them. However, the implementation exhibits divergent behavior when encountering boundary ASCII control characters or handling empty or control-only cookie names. Specifically, Coraza’s parser does not align with the normalization logic employed by many common backend web servers such as Nginx, Apache, or various application frameworks written in languages like PHP, Python, or Java. This discrepancy creates a scenario where the WAF and the backend server interpret the same Cookie header differently, leading to a state of desynchronization between the security inspection layer and the actual application logic.
The operational impact of this vulnerability is significant because it enables an unauthenticated attacker to bypass specific security rules through cookie manipulation. When an attacker crafts a malicious Cookie header containing boundary ASCII control characters or unusual naming conventions, Coraza may index or drop certain cookies under different names or values than those recognized by the backend application. For instance, if a rule is configured to inspect REQUEST_COOKIES for known attack patterns such as SQL injection payloads or cross-site scripting vectors, it relies on the WAF seeing the exact same cookie data that the application processes. Due to the parsing inconsistency, Coraza might filter out a malicious payload based on its own interpretation of the header, while simultaneously allowing the backend server to receive and process a variant of that payload under a different key or value structure. Consequently, rules targeting REQUEST_COOKIES or REQUEST_COOKIES_NAMES fail to detect the attacker data because they are analyzing a sanitized or altered version of the input, whereas the application executes logic based on the unfiltered original intent. This effectively neutralizes the protective capabilities of WAF rules that depend on accurate cookie inspection, allowing malicious requests to pass through undetected.
This type of vulnerability is classified under CWE-693 as Protection Mechanism Failure, specifically highlighting a situation where multiple components interpret security-critical data inconsistently, leading to a bypass of intended controls. In the context of the MITRE ATT&CK framework, this flaw facilitates techniques associated with Defense Evasion and potentially Command Injection or SQL Injection depending on the payload delivered via the cookie. The exploitation relies heavily on the specific backend parser in use and the scope of the WAF rules deployed by the administrator. If an organization has configured strict rule sets to block malicious cookies based on standard parsing assumptions, this inconsistency allows attackers to slip those payloads past the firewall. It is important to note that while boundary control characters are addressed in the remediation, interior control characters with inconsistent backend behavior remain outside the scope of this specific advisory, meaning organizations must maintain vigilance regarding other potential normalization discrepancies not covered by this patch.
The recommended mitigation for this issue is straightforward and involves upgrading OWASP Coraza WAF to version 3.8.1 or later. This release corrects the parsing logic in internal/cookies.ParseCookies to ensure alignment with standard backend cookie parsers, thereby eliminating the desynchronization that allows attackers to bypass security rules. Administrators should verify their deployment environments are updated promptly and review any custom rule sets that rely heavily on REQUEST_COOKIES inspection to ensure they remain effective against evolving attack vectors. Additionally, organizations should consider implementing defense-in-depth strategies by validating input at multiple layers rather than relying solely on the WAF for cookie sanitization. Regular updates of security components and continuous monitoring of traffic patterns can further reduce the risk associated with such parsing inconsistencies. By addressing this vulnerability, defenders restore the integrity of their web application firewall’s inspection capabilities, ensuring that the data analyzed matches what is ultimately processed by the backend services.