CVE-2018-6346 in Proxygen
Summary
by MITRE
A potential denial-of-service issue in the Proxygen handling of invalid HTTP2 priority settings (specifically a circular dependency). This affects Proxygen prior to v2018.12.31.00.
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Analysis
by VulDB Data Team • 05/06/2025
The vulnerability identified as CVE-2018-6346 represents a critical denial-of-service weakness within Facebook's Proxygen HTTP/2 implementation that was discovered in December 2018. This flaw specifically targets the handling of HTTP/2 priority settings and occurs when the system encounters invalid priority dependencies that create circular references within the stream dependency tree. The vulnerability affects all versions of Proxygen prior to the release dated December 31, 2018, making it a significant concern for any system utilizing this HTTP/2 library in production environments.
The technical root cause of this vulnerability stems from inadequate validation of HTTP/2 priority dependencies during the stream management process. When an HTTP/2 client sends a priority frame containing circular dependency references, the Proxygen library fails to properly detect and handle these invalid dependencies. This creates a condition where the library enters an infinite loop or consumes excessive computational resources while attempting to resolve the circular references, ultimately leading to resource exhaustion and system unresponsiveness. The flaw manifests as a failure to implement proper cycle detection mechanisms within the dependency tree management system, which is a fundamental requirement for maintaining system stability in HTTP/2 implementations.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire application stack. An attacker capable of sending malicious HTTP/2 requests with circular dependency frames can trigger a denial-of-service condition that affects the availability of services relying on Proxygen. This vulnerability particularly impacts web servers, reverse proxies, and any application infrastructure that utilizes Facebook's Proxygen library for HTTP/2 processing. The resource exhaustion can occur rapidly, potentially causing the affected service to become unresponsive or crash entirely, resulting in extended downtime and potential loss of service availability for legitimate users.
This vulnerability maps directly to CWE-691, which specifically addresses insufficient control flow management and improper handling of circular dependencies in software systems. The flaw also aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion. The improper handling of HTTP/2 priority frames demonstrates a failure in input validation and control flow management that violates fundamental security principles. Organizations using Proxygen in their infrastructure should prioritize immediate patching to address this vulnerability, as the potential for exploitation remains significant given the widespread adoption of HTTP/2 in modern web applications and the ease with which an attacker can craft malicious priority frames to trigger the condition.
Mitigation strategies should focus on upgrading to Proxygen version v2018.12.31.00 or later, which includes proper cycle detection and handling mechanisms for HTTP/2 priority dependencies. Additionally, implementing rate limiting and request validation at the network level can provide defense-in-depth protection against exploitation attempts. Network administrators should monitor for unusual patterns in HTTP/2 traffic that might indicate attempts to exploit this vulnerability, particularly focusing on priority frame handling and stream dependency management. The implementation of proper input validation and control flow management within HTTP/2 implementations should become a standard requirement for all web infrastructure components to prevent similar issues from occurring in the future.