CVE-2013-2004 in libX11
Summary
by MITRE
The (1) GetDatabase and (2) _XimParseStringFile functions in X.org libX11 1.5.99.901 (1.6 RC1) and earlier do not restrict the recursion depth when processing directives to include files, which allows X servers to cause a denial of service (stack consumption) via a crafted file.
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Analysis
by VulDB Data Team • 05/14/2021
The vulnerability identified as CVE-2013-2004 resides within the X.org libX11 library version 1.5.99.901 and earlier releases, specifically affecting the GetDatabase and _XimParseStringFile functions. This flaw represents a classic stack-based buffer overflow vulnerability that stems from inadequate recursion depth controls during file inclusion processing. The issue manifests when X servers process configuration files containing recursive include directives, creating a scenario where the stack memory consumption grows exponentially with each recursive call. The vulnerability is categorized under CWE-674, which describes "Uncontrolled Recursion" as a weakness that occurs when a function or process does not properly limit the depth of recursive calls, leading to resource exhaustion.
The technical implementation of this vulnerability exploits the lack of recursion depth limiting mechanisms within the X.org libX11 library's file parsing routines. When the GetDatabase function encounters an include directive, it recursively processes the referenced file without maintaining a counter or threshold for maximum recursion levels. Similarly, the _XimParseStringFile function exhibits the same deficiency in its parsing logic, creating a pathway for malicious actors to craft specially designed configuration files that trigger unlimited recursion. This behavior directly aligns with ATT&CK technique T1499.004, which involves resource exhaustion attacks targeting system memory through recursive processes. The vulnerability essentially creates a stack-based denial of service condition where each recursive call consumes additional stack space, eventually leading to stack overflow and system crash.
The operational impact of CVE-2013-2004 extends beyond simple service disruption, as it can be leveraged by attackers to compromise the stability of X server implementations across various Unix and Linux systems. Systems utilizing X.org libX11 for graphical interface management become vulnerable to remote or local denial of service attacks when processing untrusted configuration files. The vulnerability affects systems where X servers parse user-provided or network-accessible configuration files, including desktop environments, remote desktop solutions, and any application relying on libX11 for X11 protocol handling. This makes the vulnerability particularly dangerous in multi-user environments or systems handling untrusted input from external sources. The resource exhaustion occurs at the stack level, making it difficult to distinguish from other memory-related issues and complicating detection and mitigation efforts.
Mitigation strategies for CVE-2013-2004 require immediate patching of affected libX11 versions to implement proper recursion depth controls in the GetDatabase and _XimParseStringFile functions. System administrators should upgrade to libX11 version 1.6.0 or later, where the recursion depth limitations have been implemented. Additionally, organizations should implement configuration file validation mechanisms that restrict the inclusion of external files and establish maximum recursion limits for file processing. Network segmentation and access controls should be enforced to limit exposure of X server components to untrusted inputs. The vulnerability demonstrates the importance of implementing proper input validation and recursion depth controls in system libraries, particularly those handling configuration file parsing operations. Security monitoring should include detection of unusual stack consumption patterns and recursive file processing activities to identify potential exploitation attempts. This vulnerability serves as a critical reminder of the need for robust resource management in system libraries and the importance of adhering to secure coding practices that prevent uncontrolled recursion scenarios.