CVE-2017-12940 in unrar
Summary
by MITRE
libunrar.a in UnRAR before 5.5.7 has an out-of-bounds read in the EncodeFileName::Decode call within the Archive::ReadHeader15 function.
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Analysis
by VulDB Data Team • 02/19/2020
The vulnerability identified as CVE-2017-12940 resides within the UnRAR library version 5.5.6 and earlier, specifically manifesting in the libunrar.a component. This issue occurs during the processing of RAR archive files when the Archive::ReadHeader15 function attempts to decode file names using the EncodeFileName::Decode method. The flaw represents a classic out-of-bounds read condition that can be exploited through maliciously crafted RAR archives.
The technical implementation of this vulnerability stems from insufficient input validation within the RAR archive parsing logic. When the Archive::ReadHeader15 function processes archive headers, it calls EncodeFileName::Decode to handle filename encoding for RAR version 1.5 archives. The function fails to properly validate array bounds before accessing memory locations, allowing an attacker to craft RAR files with malformed header data that triggers memory access beyond allocated buffer boundaries. This condition falls under the Common Weakness Enumeration category CWE-129, specifically addressing improper validation of array index values.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can potentially lead to arbitrary code execution or denial of service conditions. When an application processes a maliciously crafted RAR archive using the affected UnRAR library, the out-of-bounds read can cause the application to crash or behave unpredictably. In scenarios where the vulnerable library is used in security-critical applications such as email gateways, file scanning systems, or web-based archive extraction services, this vulnerability presents a significant risk. The ATT&CK framework categorizes this as a memory corruption vulnerability that could be leveraged in exploitation chains targeting application security.
Mitigation strategies for CVE-2017-12940 involve immediate patching of the UnRAR library to version 5.5.7 or later, which contains the necessary fixes for the out-of-bounds read condition. System administrators should also implement proper input validation and sandboxing techniques when processing untrusted archive files. Additional defensive measures include configuring applications to use updated versions of the UnRAR library, implementing network-based file scanning solutions, and establishing monitoring procedures to detect potential exploitation attempts. Organizations should also consider deploying intrusion detection systems that can identify suspicious archive processing activities and maintain comprehensive backup strategies to recover from potential service disruptions caused by exploitation attempts.