CVE-2026-58436 in Gitea
Summary
by MITRE • 08/13/2026
ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests
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Analysis
by VulDB Data Team • 08/13/2026
This vulnerability involves a denial of service attack that exploits the ParseAcceptLanguage function within the Locale middleware of web applications. The flaw occurs when processing unauthenticated requests containing malformed or excessively long Accept-Language headers, leading to quadratic time complexity during request handling. The vulnerability stems from improper input validation and inefficient string parsing algorithms that scale exponentially with input length rather than maintaining linear performance characteristics. When an attacker crafts malicious Accept-Language headers with repetitive patterns or excessive nesting, the application's processing time increases dramatically, potentially causing system resource exhaustion and service unavailability for legitimate users.
The technical implementation of this vulnerability resides in how the Locale middleware handles HTTP header parsing operations. The ParseAcceptLanguage function typically processes language preference strings that follow the standard format specified in rfc3282 and rfc7231, which define the structure for Accept-Language headers. However, when these headers contain malformed data or are constructed to trigger worst-case parsing scenarios, the algorithmic complexity escalates beyond acceptable bounds. This behavior aligns with CWE-400 vulnerability classification related to resource exhaustion attacks, where computational resources become consumed proportionally to input size rather than maintaining constant or logarithmic scaling.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect entire application availability during sustained attack campaigns. Unauthenticated requests represent a particularly vulnerable surface area since they bypass normal authentication and rate limiting mechanisms that might otherwise protect against such attacks. Attackers can leverage this weakness to consume significant CPU cycles, memory resources, or thread pools through relatively small malicious requests, making the attack vector both efficient and difficult to distinguish from legitimate traffic patterns. The vulnerability particularly affects applications deployed in cloud environments where shared resource pools may experience cascading failures when individual services become overwhelmed.
Mitigation strategies should focus on implementing proper input validation and rate limiting mechanisms at the network perimeter or application level. The recommended approach involves setting maximum length constraints for Accept-Language headers, implementing early input sanitization before parsing operations, and configuring appropriate timeouts to prevent indefinite processing of malformed requests. Additionally, employing algorithmic complexity bounds and using efficient parsing libraries that handle edge cases gracefully can significantly reduce the attack surface. Organizations should also consider implementing request rate limiting based on header complexity metrics and monitoring for unusual patterns in Accept-Language header processing. The defense-in-depth strategy should include network-level controls such as web application firewalls that can detect and block suspicious header patterns, aligning with ATT&CK technique T1498 related to resource exhaustion attacks. Regular security testing including fuzzing of header parsing functions and performance benchmarking against various input sizes will help identify similar vulnerabilities in other middleware components.