CVE-2018-16384 in ModSecurity Core Rule Set
Summary
by MITRE
A SQL injection bypass (aka PL1 bypass) exists in OWASP ModSecurity Core Rule Set (owasp-modsecurity-crs) through v3.1.0-rc3 via {`a`b} where a is a special function name (such as "if") and b is the SQL statement to be executed.
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Analysis
by VulDB Data Team • 08/23/2025
The vulnerability CVE-2018-16384 represents a critical SQL injection bypass flaw within the OWASP ModSecurity Core Rule Set, specifically affecting versions through v3.1.0-rc3. This weakness allows attackers to circumvent the web application firewall's protective mechanisms by exploiting a particular pattern in SQL injection attempts. The bypass occurs through the specific syntax {`a`b} where 'a' represents a special function name such as "if" and 'b' contains the SQL statement to be executed. This technique enables malicious actors to inject SQL commands that would normally be detected and blocked by the security rules, effectively rendering the protection mechanisms ineffective.
The technical flaw stems from the ModSecurity CRS's insufficient detection logic for certain SQL injection patterns that utilize function names as part of their attack vectors. When the system encounters the pattern {`a`b} with special functions like "if", the rule set fails to properly identify the malicious intent behind this construct. This bypass mechanism operates by exploiting the way the rules evaluate and match against incoming requests, particularly when dealing with complex SQL syntax that includes function calls within the injection payload. The vulnerability specifically targets the rule engine's ability to distinguish between legitimate function usage and malicious SQL injection attempts, creating a gap in the security layer that attackers can exploit.
The operational impact of this vulnerability is significant as it allows adversaries to perform unauthorized database access and potentially execute arbitrary commands on vulnerable systems. Attackers can leverage this bypass to perform data exfiltration, data manipulation, or complete system compromise depending on the target application's database permissions and architecture. The vulnerability affects any web application protected by the affected ModSecurity CRS version, making it a widespread concern across organizations relying on this security framework. The bypass specifically targets the rule set's detection capabilities, meaning that even properly configured applications using the CRS could remain vulnerable if they haven't been updated to address this specific pattern.
Security professionals should immediately update to versions of OWASP ModSecurity Core Rule Set that address this vulnerability, as the bypass can be exploited without requiring special privileges or advanced techniques. Organizations should also implement additional monitoring and logging to detect unusual SQL patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-89 which describes improper neutralization of special elements used in SQL commands, and it relates to ATT&CK technique T1071.004 for application layer protocol manipulation. Additionally, this bypass demonstrates the ongoing challenges in developing effective web application firewall rules that can properly identify and block sophisticated SQL injection techniques while minimizing false positives. The issue underscores the importance of continuous security testing and validation of protection mechanisms against evolving attack patterns, particularly those that exploit rule set implementation gaps rather than fundamental protocol vulnerabilities.