CVE-2016-1983 in Privoxy
Summary
by MITRE
The client_host function in parsers.c in Privoxy before 3.0.24 allows remote attackers to cause a denial of service (invalid read and crash) via an empty HTTP Host header.
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Analysis
by VulDB Data Team • 07/06/2022
The vulnerability identified as CVE-2016-1983 affects Privoxy versions prior to 3.0.24 and stems from a critical flaw in the client_host function within the parsers.c file. This issue represents a classic buffer over-read condition that occurs when processing HTTP requests containing malformed Host headers. The vulnerability manifests when Privoxy encounters an empty HTTP Host header, which triggers an invalid memory read operation that ultimately leads to application crash and denial of service. The flaw exists in the HTTP request parsing logic where the software fails to properly validate or sanitize input data before attempting to process it, creating an exploitable condition that remote attackers can leverage.
The technical implementation of this vulnerability demonstrates a clear violation of input validation principles and proper memory management practices. When Privoxy processes an HTTP request with an empty Host header, the client_host function attempts to read from memory locations that may not contain valid data or may be unallocated, resulting in undefined behavior. This type of vulnerability falls under the CWE-125 weakness category, which describes out-of-bounds read conditions that occur when a program reads data past the end of a valid buffer. The lack of proper bounds checking in the parsing function creates a scenario where attacker-controlled input directly influences memory access patterns, leading to the application's termination.
From an operational perspective, this vulnerability presents a significant risk to systems relying on Privoxy for web filtering and proxy services. Remote attackers can exploit this weakness to repeatedly crash the Privoxy service, effectively rendering it unavailable to legitimate users and disrupting network operations. The denial of service impact is particularly concerning in environments where Privoxy serves as a critical component for network security or content filtering, as it can be used to disable proxy services without requiring authentication or specialized privileges. The vulnerability's exploitability is relatively straightforward since it only requires sending a malformed HTTP request with an empty Host header, making it accessible to attackers with minimal technical expertise.
The mitigation strategy for CVE-2016-1983 involves upgrading to Privoxy version 3.0.24 or later, which contains the necessary patches to properly handle empty Host headers and prevent the invalid memory reads. System administrators should prioritize this update across all affected environments, particularly in production networks where Privoxy is deployed. Additional protective measures include implementing network-level filtering to block malformed HTTP requests, deploying intrusion detection systems that can identify patterns associated with this specific vulnerability, and configuring proper monitoring to detect service disruptions that may indicate exploitation attempts. Organizations should also consider implementing redundant proxy services or fallback mechanisms to maintain network availability during patch deployment windows. The vulnerability's classification under the ATT&CK technique T1499.004 for network denial of service highlights the importance of maintaining robust network security controls and proper incident response procedures to address such threats effectively.