CVE-2017-14121 in unrar-free
Summary
by MITRE
The DecodeNumber function in unrarlib.c in unrar 0.0.1 (aka unrar-free or unrar-gpl) suffers from a NULL pointer dereference flaw triggered by a specially crafted RAR archive.
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Analysis
by VulDB Data Team • 12/27/2022
The vulnerability identified as CVE-2017-14121 represents a critical NULL pointer dereference flaw within the unrar library implementation that affects various RAR archive processing applications. This vulnerability specifically resides in the DecodeNumber function located within the unrarlib.c source file of version 0.0.1, which is commonly known as unrar-free or unrar-gpl. The flaw manifests when the library processes specially crafted RAR archive files that contain malformed or maliciously constructed data structures. The vulnerability is classified under CWE-476 which specifically addresses NULL pointer dereference conditions that can lead to application crashes or potential exploitation scenarios.
The technical implementation of this vulnerability stems from inadequate input validation within the DecodeNumber function where the code fails to properly check for null pointer conditions before attempting to dereference memory addresses. When processing a malicious RAR archive, the function encounters unexpected data patterns that cause it to attempt accessing a null memory location, resulting in an immediate application crash. This behavior represents a classic denial of service vulnerability that can be exploited by attackers who craft specific RAR files designed to trigger this condition. The flaw demonstrates poor defensive programming practices where proper error handling and input validation mechanisms are missing from the core decompression logic.
The operational impact of this vulnerability extends beyond simple application crashes, as it can be leveraged by malicious actors to disrupt services or potentially escalate to more severe security implications. Systems that rely on unrar libraries for automated RAR file processing, such as email servers, file sharing platforms, or automated backup systems, become vulnerable to service disruption attacks. The vulnerability affects a wide range of applications that depend on the unrar library for archive processing, making it particularly dangerous in enterprise environments where multiple services may be exposed to malicious archive files. Attackers can exploit this vulnerability by simply sending specially crafted RAR files to systems that process such archives, leading to unintended application termination and potential system instability.
Mitigation strategies for this vulnerability should focus on immediate patching of affected unrar library versions to address the NULL pointer dereference condition. System administrators should ensure that all instances of the unrar library are updated to versions that contain proper input validation and error handling mechanisms. Additionally, implementing proper input sanitization and validation at the application level can provide additional defense in depth measures. Network security controls such as email filtering and file validation systems should be configured to scan and block suspicious RAR archives before they reach systems that process them. This vulnerability aligns with ATT&CK technique T1204.002 which involves executing malicious code through legitimate user applications, emphasizing the importance of comprehensive application security controls and regular vulnerability assessment procedures to prevent exploitation of such flaws in widely used libraries.