CVE-2013-2175 in Linux
Summary
by MITRE
HAProxy 1.4 before 1.4.24 and 1.5 before 1.5-dev19, when configured to use hdr_ip or other "hdr_*" functions with a negative occurrence count, allows remote attackers to cause a denial of service (negative array index usage and crash) via an HTTP header with a certain number of values, related to the MAX_HDR_HISTORY variable.
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Analysis
by VulDB Data Team • 12/27/2024
The vulnerability identified as CVE-2013-2175 affects HAProxy versions prior to 1.4.24 and 1.5-dev19, representing a critical denial of service flaw that stems from improper handling of HTTP header processing. This issue specifically manifests when HAProxy is configured to utilize hdr_ip or similar "hdr_*" functions with negative occurrence counts, creating a scenario where maliciously crafted HTTP headers can trigger system instability. The vulnerability operates through the manipulation of the MAX_HDR_HISTORY variable, which governs how many header values are stored and processed within the proxy's memory management system.
The technical root cause of this vulnerability lies in the improper validation and handling of negative indices when processing HTTP headers that contain multiple values. When HAProxy encounters an HTTP header with multiple values and is configured with negative occurrence counts, the system attempts to access array elements using negative indices, which results in undefined behavior and ultimately causes the application to crash. This flaw represents a classic case of improper input validation and memory management, where the software fails to properly sanitize header values before processing them through the hdr_* functions. The negative array indexing occurs because the system does not properly validate that occurrence counts are non-negative before using them as array indices, leading to memory access violations that terminate the process.
The operational impact of this vulnerability is significant as it allows remote attackers to perform denial of service attacks against HAProxy instances without requiring authentication or privileged access. Attackers can simply craft HTTP requests containing specially formatted headers with multiple values and negative occurrence counts to trigger the crash. This vulnerability affects systems that rely on HAProxy for load balancing and reverse proxy functionality, potentially causing service disruption for legitimate users and creating opportunities for attackers to exploit the instability for further malicious activities. The vulnerability is particularly concerning in production environments where HAProxy serves as a critical component of infrastructure, as a successful attack can result in complete service interruption.
Mitigation strategies for CVE-2013-2175 involve immediate patching of affected HAProxy installations to versions 1.4.24 or 1.5-dev19 and later, which contain the necessary fixes for proper input validation. Organizations should also implement proper header validation at the network level, including monitoring for unusual header patterns and implementing rate limiting to prevent abuse of the vulnerability. Configuration changes should ensure that hdr_* functions are not used with negative occurrence counts, and administrators should consider implementing additional security controls such as header normalization and strict parsing rules. This vulnerability aligns with CWE-129, which describes improper validation of array indices, and relates to ATT&CK technique T1499.004 for denial of service through resource exhaustion, making it a critical target for immediate remediation and security hardening efforts.