CVE-2026-114460 in mod_qos
Summary
by MITRE • 10/22/2026
A flaw was found in mod_qos. An off-by-one pointer calculation error occurs when merging request body parameters with an existing URL query, which truncates the query string during security evaluation while leaving the actual request unchanged. An unauthenticated remote attacker could exploit this vulnerability by submitting a crafted request that conceals prohibited values from inspection, resulting in a bypass of configured security rules.
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Analysis
by VulDB Data Team • 10/22/2026
The mod_qos module for Apache HTTP Server contains a critical logic flaw rooted in an off-by-one pointer calculation error during the processing of incoming HTTP requests. This specific implementation defect manifests when the server attempts to merge request body parameters with existing URL query strings, particularly in scenarios where both components are present within a single request. The vulnerability arises from incorrect memory indexing or boundary checking that fails to account for the full length of the concatenated string, leading to an unintended truncation of the resulting data structure before it is passed to subsequent security evaluation layers. This discrepancy creates a divergence between what the application logic perceives as the complete input and what is actually transmitted by the client, establishing a fundamental inconsistency in how request parameters are interpreted versus how they are processed for access control decisions.
From an operational perspective, this vulnerability allows unauthenticated remote attackers to bypass configured security rules through crafted HTTP requests that exploit the truncation behavior. By carefully constructing payloads that leverage the off-by-one error, an attacker can ensure that prohibited or malicious values remain hidden from the inspection mechanisms of mod_qos while still being delivered intact to the backend application server. This effectively neutralizes protective measures such as rate limiting, request size restrictions, or content filtering rules that rely on accurate parsing of query parameters and body data. The security evaluation layer sees a sanitized or truncated version of the request that appears compliant with policy, whereas the actual underlying transaction contains forbidden elements, thereby enabling unauthorized access, data exfiltration, or further exploitation depending on the specific protections being bypassed.
This vulnerability aligns closely with CWE-193 Off-by-One Error and CWE-20 Improper Input Validation, as it stems from a failure to correctly handle input boundaries during string manipulation operations. In terms of offensive security frameworks, this behavior is characteristic of ATT&CK technique T1190 Exploit Public-Facing Application, where attackers leverage flaws in internet-facing software to bypass defenses and gain initial access or escalate privileges without authentication. The impact extends beyond simple rule evasion; it undermines the integrity of web application firewalls and reverse proxy security controls that depend on accurate request reconstruction for threat detection.
Mitigation strategies must prioritize immediate patching of the mod_qos module to a version where this pointer calculation logic has been corrected by upstream developers. Administrators should verify their Apache configurations ensure that all modules are updated to address known CVEs related to input parsing and boundary checks. In environments where upgrading is not immediately feasible, compensating controls such as implementing strict request validation at the network perimeter using next-generation firewalls or web application firewalls with deep packet inspection capabilities can help detect anomalous payload structures. Additionally, enabling comprehensive logging of HTTP requests allows for monitoring of patterns that may indicate exploitation attempts involving truncated query strings or mismatched body parameters, facilitating rapid incident response and forensic analysis to assess potential compromise scope.