CVE-2018-10184 in HAProxy
Summary
by MITRE
An issue was discovered in HAProxy before 1.8.8. The incoming H2 frame length was checked against the max_frame_size setting instead of being checked against the bufsize. The max_frame_size only applies to outgoing traffic and not to incoming, so if a large enough frame size is advertised in the SETTINGS frame, a wrapped frame will be defragmented into a temporary allocated buffer where the second fragment may overflow the heap by up to 16 kB. It is very unlikely that this can be exploited for code execution given that buffers are very short lived and their addresses not realistically predictable in production, but the likelihood of an immediate crash is absolutely certain.
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Analysis
by VulDB Data Team • 03/11/2023
The vulnerability identified as CVE-2018-10184 represents a critical heap buffer overflow condition within HAProxy versions prior to 1.8.8, specifically affecting the HTTP/2 protocol implementation. This flaw stems from an improper validation mechanism that incorrectly processes incoming HTTP/2 frames by comparing their length against the max_frame_size configuration parameter rather than the bufsize setting. The fundamental issue arises from the misapplication of frame size validation logic where outgoing traffic parameters are incorrectly used to validate incoming traffic, creating a dangerous mismatch in buffer management. The HTTP/2 protocol specification defines max_frame_size as a parameter that governs the maximum size of frames that can be sent from the server to the client, making it inherently inappropriate for validating incoming frame sizes. This misconfiguration creates a scenario where maliciously crafted HTTP/2 SETTINGS frames can advertise arbitrarily large frame sizes, leading to buffer overflow conditions during frame defragmentation processes.
The technical exploitation of this vulnerability occurs during the defragmentation of wrapped HTTP/2 frames, where the system allocates temporary buffers to handle fragmented data segments. When an attacker sends a SETTINGS frame advertising a large frame size, subsequent frames that exceed normal buffer boundaries will trigger the overflow condition. The overflow affects heap memory allocation where the second fragment of a wrapped frame can overwrite adjacent memory regions, potentially causing memory corruption that leads to immediate system instability. The maximum overflow potential reaches up to 16 kilobytes, which represents a significant memory corruption vector that can compromise the integrity of the application's heap memory management. This particular vulnerability manifests as a deterministic crash condition rather than a potential code execution vector, as the heap corruption typically results in immediate application termination. The short-lived nature of the temporary buffers and the unpredictable memory addresses in production environments significantly reduce the likelihood of successful exploitation for remote code execution, but the certainty of system crash makes this a severe availability threat.
From a cybersecurity perspective, this vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a classic case of improper input validation within network protocol implementations. The flaw demonstrates poor defensive programming practices where the same configuration parameters are incorrectly applied across different traffic directions without proper consideration of protocol semantics. The attack surface is particularly concerning for high-availability systems that rely on HAProxy as a load balancer or reverse proxy, as the deterministic crash behavior can be easily weaponized for denial-of-service attacks. Organizations utilizing HTTP/2 traffic handling through HAProxy are particularly vulnerable to this attack vector, especially in environments where the proxy serves as a critical infrastructure component. The vulnerability's impact extends beyond simple service disruption to potentially compromise the reliability of entire application stacks that depend on HAProxy for traffic management. According to ATT&CK framework, this vulnerability maps to T1499.004, Network Denial of Service, and T1595.001, Network Device Software, as it exploits weaknesses in network infrastructure software. The exploitability is enhanced in environments where HTTP/2 is actively used, making it a significant concern for organizations maintaining modern web infrastructure that leverages HTTP/2 protocol features.
The recommended mitigation strategy involves immediate upgrade to HAProxy version 1.8.8 or later, which contains the necessary patch to correct the frame size validation logic. System administrators should also implement monitoring for unusual SETTINGS frame behavior and consider implementing rate limiting for HTTP/2 connections to reduce the attack surface. Additional defensive measures include configuring appropriate buffer size limits and implementing network segmentation to isolate critical services from potentially compromised HTTP/2 traffic. Organizations should conduct thorough vulnerability assessments to identify all systems running vulnerable HAProxy versions and establish emergency response procedures for rapid patch deployment. The vulnerability highlights the importance of proper protocol implementation validation and the necessity of maintaining up-to-date security patches for critical infrastructure components. Regular security audits of network infrastructure software should include thorough examination of protocol handling mechanisms to prevent similar issues from arising in the future.