CVE-2021-20210 in Privoxy
Summary
by MITRE • 03/25/2021
A flaw was found in Privoxy in versions before 3.0.29. Memory leak in the show-status CGI handler when no filter files are configured can lead to a system crash.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2021-20210 represents a critical memory management flaw within the Privoxy web proxy software ecosystem. This issue affects versions prior to 3.0.29 and specifically targets the show-status CGI handler component that is responsible for displaying system status information. The flaw manifests as a memory leak condition that occurs when the CGI handler attempts to process requests in environments where no filter files have been configured, creating a scenario where allocated memory resources are not properly released back to the system. This particular vulnerability falls under the category of memory corruption issues and aligns with CWE-401, which specifically addresses improper management of memory allocation and deallocation in software applications. The memory leak vulnerability creates an exploitable condition that can be leveraged by attackers to consume system resources progressively until the system becomes unresponsive or crashes entirely.
The technical implementation of this vulnerability occurs within the CGI handler's response processing logic where the software fails to properly clean up allocated memory structures when filter files are absent from the configuration. When a request is made to the show-status endpoint without any filter configuration, the memory allocation for status information processing continues to accumulate without subsequent deallocation, leading to progressive memory consumption. This behavior directly impacts the system's ability to maintain stable operations and can result in denial of service conditions that affect legitimate users of the proxy service. The vulnerability's exploitation requires minimal privileges and can be triggered through simple HTTP requests to the affected CGI endpoint, making it particularly dangerous in production environments where continuous availability is critical. From an operational security perspective, this vulnerability represents a significant risk to organizations relying on Privoxy for web filtering and privacy protection services.
The operational impact of CVE-2021-20210 extends beyond simple resource exhaustion to encompass broader system stability and availability concerns. When exploited, the memory leak can cause the Privoxy service to become unresponsive, requiring manual intervention to restart the service and potentially leading to extended periods of service disruption. Organizations using Privoxy in high-traffic environments face increased risk of cascading failures that could impact downstream applications and services dependent on the proxy functionality. The vulnerability's characteristics align with attack patterns described in the MITRE ATT&CK framework under the T1499 category of Network Denial of Service, where attackers can exploit software weaknesses to disrupt network services and availability. System administrators may observe gradual performance degradation before complete service failure, making early detection and mitigation challenging. The vulnerability's presence in the CGI handler component also raises concerns about potential information disclosure or further exploitation paths that could be leveraged in combination with other vulnerabilities.
Mitigation strategies for CVE-2021-20210 focus primarily on immediate software upgrades to version 3.0.29 or later, which contain the necessary patches to address the memory leak condition. Organizations should prioritize patch management procedures to ensure all Privoxy instances are updated promptly, particularly in environments where the affected CGI handler is exposed to external networks. Network segmentation and access controls should be implemented to limit exposure of the CGI endpoints to trusted users only, reducing the attack surface for potential exploitation. Monitoring systems should be configured to detect unusual memory consumption patterns or service disruptions that could indicate exploitation attempts. Security teams should also consider implementing automated patch deployment mechanisms to ensure rapid remediation across all affected systems. The vulnerability's classification as a memory leak issue also suggests that organizations should implement robust memory monitoring and alerting procedures to detect similar conditions in other applications. Additionally, regular security assessments should be conducted to identify and remediate similar memory management issues that may exist in other components of the web proxy infrastructure, aligning with industry best practices for maintaining secure system configurations.