CVE-2016-1982 in Privoxy
Summary
by MITRE
The remove_chunked_transfer_coding function in filters.c in Privoxy before 3.0.24 allows remote attackers to cause a denial of service (invalid read and crash) via crafted chunk-encoded content.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 07/06/2022
The vulnerability identified as CVE-2016-1982 affects Privoxy versions prior to 3.0.24, specifically targeting the remove_chunked_transfer_coding function within the filters.c module. This issue represents a critical flaw in the proxy server's handling of HTTP chunked transfer encoding, which is a standard method for transferring data in HTTP protocol where data is sent in a series of chunks. The vulnerability arises from inadequate input validation and processing of malformed chunked content, creating a scenario where remote attackers can exploit this weakness to disrupt service availability.
The technical implementation of this vulnerability stems from the function's failure to properly validate chunked transfer encoding data before processing it. When Privoxy encounters crafted chunk-encoded content, the remove_chunked_transfer_coding function attempts to parse and remove the chunked transfer coding headers without sufficient bounds checking or error handling. This leads to invalid memory reads and subsequent application crashes, as the function accesses memory locations that are either uninitialized or improperly allocated. The flaw essentially creates a buffer overread condition where the application processes data beyond its allocated memory boundaries, resulting in unpredictable behavior and system instability. This vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and represents a classic example of improper input validation in network protocol handling code.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attack vectors. Remote attackers can leverage this weakness to perform denial of service attacks against Privoxy instances, causing them to crash and restart repeatedly, thereby denying legitimate users access to the proxy service. In environments where Privoxy serves as a critical filtering or privacy protection mechanism, such attacks could compromise network security posture and availability. The vulnerability is particularly concerning because it requires no authentication or privileged access to exploit, making it an attractive target for automated attack tools. From an adversarial perspective, this flaw maps to ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a low-effort, high-impact method for disrupting services that rely on proper HTTP handling.
Mitigation strategies for CVE-2016-1982 primarily focus on upgrading to Privoxy version 3.0.24 or later, which includes proper input validation and memory handling for chunked transfer encoding. Organizations should also implement network monitoring to detect unusual patterns of service disruption that might indicate exploitation attempts. Additional protective measures include configuring network-level firewalls to restrict access to Privoxy services, implementing intrusion detection systems that can identify malformed HTTP traffic patterns, and maintaining regular security updates for all proxy and filtering software components. Security teams should also consider deploying application-level firewalls or web application firewalls that can detect and block malicious chunked encoding patterns before they reach the Privoxy service. The vulnerability serves as a reminder of the critical importance of proper input validation in network protocol implementations and demonstrates how seemingly minor flaws in HTTP handling code can result in significant availability impacts.