A major denial of service vulnerability has been found in ModSecurity, one of the extensively deployed open-source internet utility firewall (WAF) engines used to guard Apache, IIS, and Nginx internet servers.
The vulnerability, designated as CVE-2025-48866, impacts all ModSecurity variations previous to 2.9.10 and permits attackers to crash programs via exploitation of the sanitiseArg and sanitizeArg actions.
This high-severity flaw carries a CVSS rating of seven.5, highlighting the numerous threat it poses to organizations counting on ModSecurity for internet utility safety.
ModSecurity DoS Flaw
The newly recognized vulnerability stems from extreme platform useful resource consumption inside a loop, categorised beneath CWE-1050 weak spot enumeration.
When ModSecurity processes guidelines containing the sanitiseArg or sanitizeArg actions, the system turns into susceptible to including an extreme variety of arguments, in the end resulting in denial of service circumstances.
This flaw particularly targets the argument sanitization performance designed to masks delicate knowledge like passwords in audit logs.
The vulnerability vector is especially regarding as it may be exploited remotely over networks with out requiring authentication or person interplay.
In keeping with the CVSS 3.1 vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, attackers can obtain excessive availability influence whereas the assault complexity stays low.
Nonetheless, the exploitation requires very particular circumstances, because the vulnerability solely manifests when guidelines explicitly specify arguments for the sanitization actions, , akin to within the configuration instance:
The technical root trigger lies within the inefficient processing of argument sanitization inside mod_security2.
When a rule makes use of the sanitiseArg motion, the system examines all parsed arguments and calls the sanitization operate repeatedly for every matching argument title.
In situations the place a lot of arguments match the required standards, this creates a resource-intensive loop that may overwhelm system sources.
As an illustration, if an utility processes 500 arguments via the ARGS variable and all match the sanitization standards, the motion would execute 500 occasions consecutively.
Every execution provides matching argument names to the sanitization listing, creating cumulative useful resource consumption that may escalate to system crash ranges.
This conduct mirrors the beforehand disclosed vulnerability CVE-2025-47947, indicating a sample of comparable vulnerabilities inside the ModSecurity codebase.
Importantly, this vulnerability solely impacts mod_security2 implementations and doesn’t influence libmodsecurity3, because the latter doesn’t assist the problematic sanitiseArg actions. This distinction is essential for organizations planning their safety response methods.
Threat FactorsDetailsAffected ProductsModSecurity (mod_security2) variations previous to 2.9.10ImpactDenial of ServiceExploit Prerequisites1. Guidelines utilizing sanitiseArg/sanitizeArg with specified arguments2. Means to inject extreme matching argumentsCVSS 3.1 Score7.5 (Excessive)
Mitigation Methods
Organizations can implement quick safety via a number of approaches. The first advice entails upgrading to ModSecurity model 2.9.10, which accommodates the official repair for this vulnerability.
The event workforce at ModSecurity found this flaw throughout a complete code evaluate following their earlier vulnerability disclosure, demonstrating their dedication to proactive safety measures.
For environments the place quick upgrading is just not possible, directors can implement a workaround by avoiding guidelines that include the sanitiseArg or sanitizeArg actions.
This non permanent measure eliminates the assault vector whereas organizations put together for system updates.
Safety groups ought to audit their present ModSecurity configurations to establish any guidelines using the susceptible actions and assess their publicity threat.
Organizations also needs to take into account implementing extra monitoring for uncommon useful resource consumption patterns which may point out exploitation makes an attempt.
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