CVE-2021-20214 in Privoxy
Summary
by MITRE • 03/25/2021
A flaw was found in Privoxy in versions before 3.0.29. Memory leaks in the client-tags CGI handler when client tags are configured and memory allocations fail can lead to a system crash.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2021-20214 resides within the Privoxy web proxy software, specifically affecting versions prior to 3.0.29. This flaw manifests as a memory leak condition within the client-tags CGI handler component of the application. The issue becomes particularly critical when client tags are configured within the system and subsequent memory allocation operations fail during processing. The memory leak occurs in the context of web proxy operations where client tags are used to manage and categorize different user groups or access levels. This vulnerability represents a significant concern for organizations relying on Privoxy for web filtering and privacy protection services.
The technical implementation of this flaw involves the improper handling of memory resources within the client-tags CGI handler module. When the system attempts to allocate memory for processing client tag configurations and these allocation attempts fail, the application fails to properly release previously allocated memory segments. This memory leak condition accumulates over time, eventually consuming available system resources and leading to application instability. The vulnerability is particularly dangerous because it can be triggered through normal web proxy operations when client tags are configured and active. The flaw demonstrates poor resource management practices and indicates inadequate error handling within the memory allocation pathways of the CGI handler component.
The operational impact of CVE-2021-20214 extends beyond simple resource exhaustion to potentially disrupt critical network services. Organizations utilizing Privoxy for web filtering, content blocking, or privacy protection may experience unexpected service interruptions when this vulnerability is exploited. The system crash resulting from memory exhaustion can affect multiple users simultaneously, particularly in environments where Privoxy serves as a central filtering point for large user bases. This vulnerability creates a persistent risk that can be exploited by attackers to perform denial-of-service attacks against proxy services, making it particularly concerning for enterprise environments where continuous availability is critical. The impact is further compounded by the fact that the vulnerability can be triggered through normal operational activities without requiring special privileges or complex attack vectors.
Mitigation strategies for this vulnerability primarily focus on immediate software updates to version 3.0.29 or later, which contains the necessary patches to address the memory leak conditions. Organizations should prioritize deployment of the updated software across all affected systems to eliminate the risk of exploitation. Additionally, system administrators should implement monitoring solutions to track memory usage patterns and detect potential memory leak conditions before they escalate to system crashes. Configuration reviews should include verifying that client tags are properly implemented and that unnecessary client tag configurations are removed from systems where they are not required. This vulnerability aligns with CWE-401, which describes improper management of memory allocation and deallocation, and represents a typical example of how resource management flaws can lead to system stability issues. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial-of-service tactics, as attackers can leverage the memory leak to disrupt services or potentially gain elevated system access through sustained resource exhaustion attacks.