CVE-2026-114457 in mod_qos
Summary
by MITRE • 10/22/2026
A flaw was found in mod_qos. An unauthenticated remote attacker could cause a Denial of Service (DoS) by sending a specially crafted JSON request when JSON body filtering is enabled. Due to improper string termination during the processing of percent-encoded input, the module reads past allocated memory boundaries, which can cause an Apache worker process to crash.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified in mod_qos represents a critical security flaw within one of the most widely deployed HTTP request control modules for the Apache web server ecosystem. This specific issue stems from improper string termination handling during the processing of percent-encoded input data, which directly leads to an out-of-bounds memory read condition. When JSON body filtering is enabled, as configured by administrators to inspect or restrict incoming payloads based on their content type and structure, the module fails to correctly validate the boundaries of strings that have undergone URL decoding. This failure allows an unauthenticated remote attacker to craft a specially formatted JSON request containing percent-encoded characters that, when processed, cause the application logic to read beyond allocated memory buffers. The consequence of this improper string termination is severe, as it triggers a segmentation fault or similar critical error within the Apache worker process responsible for handling the malicious request.
From an operational perspective, the immediate impact of this vulnerability is a Denial of Service against the affected web server infrastructure. Because mod_qos operates at the connection and request level before many other application-layer protections are engaged, it serves as a primary line of defense in high-traffic environments. The crash of an Apache worker process results in the inability to serve legitimate requests through that specific thread or process, leading to increased latency, dropped connections, and potentially complete service unavailability if multiple workers are compromised simultaneously. This is particularly dangerous because the attack requires no authentication, allowing any external actor on the network to trigger the condition simply by sending a single malformed HTTP request with an appropriate JSON payload. The reliability of mod_qos as a traffic shaping tool is thus undermined, turning a security feature into a vector for service disruption.
In terms of industry-standard classification frameworks, this vulnerability aligns closely with CWE-125, which describes Out-of-bounds Read vulnerabilities where software reads data past the end or before the beginning of the intended buffer. The mechanism involves improper handling of encoded input strings that leads to memory boundary violations. Furthermore, within the MITRE ATT&CK framework, this exploit technique falls under Tactic TA0004 Impact and specifically relates to techniques such as Resource Hijacking or Denial of Service via application layer attacks. Attackers leverage these types of flaws in web server modules because they are often enabled by default for performance optimization or security hardening purposes like JSON filtering, making them a high-value target for automated scanning tools that seek to disrupt services without needing valid credentials.
Mitigation strategies must focus on immediate patching and configuration review. Administrators should update mod_qos to the latest stable version where this string termination logic has been corrected by the developers. If updating is not immediately feasible due to compatibility constraints, disabling JSON body filtering within the mod_qos configuration serves as an effective temporary workaround, although this reduces the module's ability to inspect payload contents for other potential threats like injection attacks. Additionally, deploying a Web Application Firewall in front of Apache can help filter out malformed requests before they reach the vulnerable module, providing an additional layer of defense against exploitation attempts. Regular auditing of server configurations and keeping all third-party modules up to date are essential practices to maintain the integrity and availability of web services exposed to untrusted networks.