CVE-2020-35502 in Privoxy
Summary
by MITRE • 03/25/2021
A flaw was found in Privoxy in versions before 3.0.29. Memory leaks when a response is buffered and the buffer limit is reached or Privoxy is running out of memory can lead to a system crash.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2020-35502 represents a critical memory management flaw within the Privoxy web proxy software that affects versions prior to 3.0.29. This issue manifests as memory leaks that occur under specific operational conditions, creating a potential denial of service scenario that can compromise system stability and availability. The flaw is particularly concerning given Privoxy's role as a popular filtering proxy server that many organizations rely upon for web content filtering and privacy protection.
The technical implementation of this vulnerability stems from improper memory handling when Privoxy processes web responses that exceed predefined buffer limits or when the system encounters memory exhaustion during normal operation. When response buffering reaches its maximum capacity or when Privoxy operates under memory constraints, the software fails to properly release allocated memory resources, resulting in progressive memory consumption that eventually leads to system instability and potential crashes. This behavior aligns with CWE-401, which categorizes memory leaks as a fundamental weakness in memory management that can lead to resource exhaustion and system failure. The vulnerability demonstrates a classic pattern of inadequate resource cleanup in response handling code paths, where allocated buffers are not properly deallocated when conditions such as buffer overflow or memory scarcity occur.
The operational impact of CVE-2020-35502 extends beyond simple service disruption to encompass broader system reliability concerns for organizations that depend on Privoxy for their web filtering infrastructure. When memory leaks accumulate over time, they can gradually consume available system resources until the proxy service becomes unresponsive or crashes entirely, potentially disrupting network access for all users relying on that filtering infrastructure. This vulnerability particularly affects environments where Privoxy serves high-volume traffic or where long-running proxy sessions are common, as the memory consumption grows progressively with each affected response processing cycle. The attack surface is further expanded by the fact that this vulnerability can be triggered through normal web browsing activities without requiring special privileges or complex exploitation techniques, making it a significant concern for both enterprise and home network environments.
Organizations should prioritize immediate remediation by upgrading to Privoxy version 3.0.29 or later, which contains the necessary patches to address the memory leak conditions. System administrators should also implement monitoring solutions to track memory consumption patterns and establish alerting mechanisms for unusual resource usage that could indicate the vulnerability's exploitation. Additional mitigations include implementing proper resource limits on Privoxy processes, configuring buffer size restrictions, and maintaining regular system updates to prevent similar issues from arising. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004, which covers network denial of service attacks through resource exhaustion, and represents a common exploitation vector that attackers can leverage to disrupt services. Organizations should also consider implementing network segmentation and access controls to limit potential attack surfaces and ensure that proxy services are properly isolated from critical network infrastructure.