CVE-2021-20216 in Privoxy
Summary
by MITRE • 03/25/2021
A flaw was found in Privoxy in versions before 3.0.31. A memory leak that occurs when decompression fails unexpectedly may lead to a denial of service. The highest threat from this vulnerability is to system availability.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2021-20216 represents a critical memory leak issue within the Privoxy web proxy software ecosystem. This flaw exists in versions prior to 3.0.31 and specifically manifests during decompression operations when unexpected failures occur. Privoxy serves as a non-caching web proxy that filters web content and provides privacy protection, making it a crucial component in many network security infrastructures. The memory leak vulnerability arises from inadequate memory management practices during the decompression process, where the software fails to properly release allocated memory resources when decompression operations encounter errors or unexpected conditions.
The technical implementation of this vulnerability stems from improper error handling within Privoxy's decompression routines. When decompression fails unexpectedly, the system should gracefully release all allocated memory resources and return to a stable state. However, in affected versions, memory allocated for decompression operations is not properly deallocated, leading to progressive memory consumption over time. This memory leak directly impacts the proxy's ability to maintain stable operations, as available system memory gradually diminishes with each decompression failure event. The vulnerability operates at the application layer and can be triggered through malformed compressed content or network conditions that cause decompression to fail, making it particularly dangerous in high-traffic environments where multiple decompression operations occur simultaneously.
The operational impact of CVE-2021-20216 poses significant threats to system availability and service continuity. As memory consumption increases progressively due to the leak, the proxy service eventually becomes unresponsive or crashes entirely, resulting in complete denial of service for all users relying on the proxy infrastructure. This vulnerability particularly affects organizations that depend on Privoxy for content filtering, privacy protection, and web traffic management, as the denial of service can disrupt business operations and compromise network security posture. The threat level is classified as high due to the direct correlation between memory consumption and system availability, with potential for cascading effects in larger network infrastructures where Privoxy serves as a critical intermediary component.
Mitigation strategies for this vulnerability require immediate deployment of Privoxy version 3.0.31 or later, which includes proper memory management fixes for decompression error handling. Network administrators should conduct comprehensive vulnerability assessments to identify all systems running affected Privoxy versions and implement patch management procedures to ensure timely updates. Additionally, monitoring systems should be enhanced to track memory usage patterns and detect anomalous consumption that may indicate exploitation of this vulnerability. Organizations should also consider implementing redundant proxy services or failover mechanisms to maintain availability during patch deployment windows. This vulnerability aligns with CWE-401, which addresses improper handling of memory allocation failures, and corresponds to ATT&CK technique T1499.004, focusing on network denial of service attacks that target system availability through resource exhaustion.