CVE-2020-25219 in libproxy
Summary
by MITRE
url::recvline in url.cpp in libproxy 0.4.x through 0.4.15 allows a remote HTTP server to trigger uncontrolled recursion via a response composed of an infinite stream that lacks a newline character. This leads to stack exhaustion.
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Analysis
by VulDB Data Team • 09/10/2020
The vulnerability identified as CVE-2020-25219 resides within the libproxy library version 0.4.x through 0.4.15, specifically in the url::recvline function located in url.cpp. This flaw represents a critical security issue that can be exploited by remote HTTP servers to cause stack exhaustion through uncontrolled recursion. The vulnerability stems from the library's improper handling of HTTP responses that contain infinite data streams without newline characters, creating a condition where the recursive parsing function continues indefinitely until system resources are exhausted.
The technical implementation of this vulnerability involves the url::recvline function attempting to read data from HTTP responses in a recursive manner without proper bounds checking or termination conditions. When encountering an HTTP response that does not contain newline characters, the function enters an infinite loop where it continuously attempts to read data without ever reaching a proper termination point. This recursive behavior consumes stack memory rapidly, leading to stack exhaustion and ultimately causing the application to crash or become unresponsive. The vulnerability is classified under CWE-674 which deals with uncontrolled recursion, specifically highlighting the dangerous nature of recursive functions that lack proper termination conditions.
From an operational perspective, this vulnerability poses significant risks to any system that utilizes libproxy for proxy configuration management, particularly in web browsers, network management tools, and applications that process HTTP responses. The impact extends beyond simple service disruption to potentially enabling denial of service attacks that can affect entire network infrastructures. Attackers can craft malicious HTTP responses that exploit this recursion flaw, causing applications using libproxy to consume excessive memory and eventually crash. This vulnerability affects systems that rely on the library for proxy auto-configuration and can be particularly dangerous in environments where proxy configuration is automatically handled, such as enterprise networks or browser-based applications.
The attack surface for this vulnerability is broad, encompassing any application or system that depends on libproxy for HTTP proxy handling, including but not limited to web browsers, network monitoring tools, and system management applications. The exploitation requires a remote HTTP server to send a specially crafted response that lacks newline characters, making it particularly insidious as it can be triggered through normal web browsing activities or automated network scanning. The vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and more specifically with T1059.007 which addresses command and scripting interpreter execution through recursive or iterative processes.
Mitigation strategies for CVE-2020-25219 involve immediate patching of libproxy to version 0.4.16 or later, which contains the necessary fixes to prevent uncontrolled recursion. Organizations should also implement network-level controls such as proxy server configurations that can detect and block malformed HTTP responses, as well as monitoring systems that can identify unusual memory consumption patterns that may indicate exploitation attempts. Additionally, application developers should consider implementing bounds checking and timeout mechanisms when processing HTTP responses, and system administrators should regularly update all components that utilize libproxy to ensure protection against this and similar vulnerabilities. The fix typically involves implementing proper recursion depth limits and ensuring that the recvline function terminates appropriately when encountering data streams without newline characters, preventing the stack exhaustion that leads to system instability and potential denial of service conditions.