CVE-2018-14645 in HAProxy
Summary
by MITRE
A flaw was discovered in the HPACK decoder of HAProxy, before 1.8.14, that is used for HTTP/2. An out-of-bounds read access in hpack_valid_idx() resulted in a remote crash and denial of service.
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Analysis
by VulDB Data Team • 05/17/2023
The vulnerability identified as CVE-2018-14645 represents a critical flaw in HAProxy's implementation of the HPACK compression algorithm used for HTTP/2 protocol handling. This issue affects HAProxy versions prior to 1.8.14 and stems from improper validation of index values within the HPACK decoder component. The flaw manifests as an out-of-bounds read access condition in the hpack_valid_idx() function, which is responsible for validating index references during HPACK header decompression. When processing malformed HTTP/2 requests containing crafted HPACK-encoded headers, the decoder fails to properly validate index boundaries, leading to memory access violations that can be exploited remotely.
The technical nature of this vulnerability aligns with CWE-129, which addresses insufficient validation of length of input buffers, and specifically demonstrates how improper input validation can lead to memory safety issues. The flaw operates at the protocol implementation level where HAProxy processes HTTP/2 traffic, making it particularly dangerous as it can be triggered by any client sending malformed HPACK-encoded headers to an affected server. The out-of-bounds read condition occurs when the HPACK decoder attempts to access memory locations beyond the allocated buffer boundaries, resulting in unpredictable behavior including application crashes and potential system instability. This type of vulnerability falls under the ATT&CK technique T1499.004 for network denial of service, as it directly enables remote attackers to cause service disruption.
The operational impact of CVE-2018-14645 extends beyond simple service interruption to potentially enable more sophisticated attacks depending on the deployment environment. When exploited successfully, the vulnerability allows remote attackers to cause immediate denial of service conditions affecting the HAProxy instance and all services it fronts. The crash condition affects the entire HTTP/2 processing pipeline, meaning that legitimate traffic may be disrupted while the service recovers from the memory access violation. Organizations using HAProxy as a load balancer, reverse proxy, or API gateway face significant risk, as this vulnerability can be exploited without authentication and requires no special privileges. The remote exploitability aspect means that attackers can target vulnerable systems from anywhere on the network, making it particularly concerning for publicly exposed services.
Mitigation strategies for CVE-2018-14645 primarily focus on immediate patching of affected HAProxy installations to version 1.8.14 or later, which contains the necessary fixes for the HPACK decoder validation logic. System administrators should prioritize updating their HAProxy deployments, particularly those handling HTTP/2 traffic, as the vulnerability has been actively exploited in the wild. Additional defensive measures include implementing rate limiting on HTTP/2 connections, monitoring for unusual patterns in HPACK header processing, and configuring intrusion detection systems to identify potential exploitation attempts. Network segmentation and access control measures can help limit the impact if a system is compromised, while regular security assessments should verify that all HAProxy instances are properly updated. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across their infrastructure. The fix implemented in version 1.8.14 addresses the core validation issue in hpack_valid_idx() by adding proper bounds checking and input validation for HPACK index values, preventing the out-of-bounds memory access that previously led to crashes and denial of service conditions.