CVE-2021-20212 in Privoxy
Summary
by MITRE • 03/25/2021
A flaw was found in Privoxy in versions before 3.0.29. Memory leak if multiple filters are executed and the last one is skipped due to a pcre error leading to a system crash.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2021-20212 represents a critical memory management flaw within the Privoxy web proxy software that affects versions prior to 3.0.29. This issue manifests when the proxy processes multiple filter rules and encounters a pcre (Perl Compatible Regular Expressions) error during the execution of the final filter in a sequence. The flaw creates a condition where allocated memory resources are not properly released, resulting in a gradual consumption of system memory until the application becomes unstable and crashes. This vulnerability directly impacts the reliability and availability of the proxy service, potentially disrupting network traffic routing and filtering operations that depend on Privoxy.
The technical implementation of this vulnerability stems from improper memory deallocation logic within Privoxy's filter processing engine. When multiple filters are applied to web content and the final filter fails due to a pcre compilation or execution error, the software fails to execute the necessary cleanup procedures that would normally release previously allocated memory blocks. This memory leak condition accumulates over time as the proxy continues processing requests, eventually leading to resource exhaustion and system instability. The vulnerability operates at the application layer and specifically affects the regular expression engine integration within the proxy's filtering mechanism, making it particularly dangerous in environments where Privoxy serves as a critical network component.
From an operational impact perspective, this vulnerability creates significant risks for organizations relying on Privoxy for web filtering, privacy protection, and network traffic management. The system crash resulting from memory exhaustion can lead to complete service disruption, forcing administrators to restart the proxy service manually and potentially causing temporary loss of network filtering capabilities. In high-traffic environments, the memory leak can escalate quickly, leading to system instability that may affect other network services running on the same infrastructure. The vulnerability also poses risks to availability-based attacks where malicious actors could exploit the memory leak to perform denial-of-service operations against Privoxy instances, particularly in scenarios where the proxy serves as a gateway for multiple users or applications.
The mitigation strategy for CVE-2021-20212 centers on upgrading to Privoxy version 3.0.29 or later, which includes the necessary memory management fixes to properly handle filter execution errors and ensure proper resource cleanup. System administrators should prioritize this update across all affected environments, particularly in production networks where Privoxy serves critical filtering functions. Additionally, monitoring systems should be implemented to track memory usage patterns of Privoxy processes, enabling early detection of potential memory leak conditions before they escalate to system crashes. Network administrators should also consider implementing redundant proxy configurations or alternative filtering solutions as part of their disaster recovery planning to maintain service availability during patch deployment or in case of unexpected failures. This vulnerability aligns with CWE-401, which addresses improper handling of memory allocation and deallocation, and could be leveraged in ATT&CK tactics related to denial-of-service and service disruption.