CVE-2017-12941 in unrar
Summary
by MITRE
libunrar.a in UnRAR before 5.5.7 has an out-of-bounds read in the Unpack::Unpack20 function.
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Analysis
by VulDB Data Team • 02/19/2020
The vulnerability identified as CVE-2017-12941 affects libunrar.a, a core component of the UnRAR archiving utility that handles RAR file decompression operations. This flaw exists in versions prior to 5.5.7 and represents a critical security issue that could be exploited to disrupt system operations or potentially execute arbitrary code. The vulnerability specifically manifests within the Unpack::Unpack20 function, which is responsible for processing RAR file compression algorithms. This function processes data streams during decompression and contains a flaw that allows for unauthorized memory access beyond the bounds of allocated buffers.
The technical nature of this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions where a program attempts to read memory locations beyond the allocated buffer boundaries. The flaw occurs during the decompression of maliciously crafted RAR archives that contain specially constructed data sequences. When the Unpack::Unpack20 function processes these malformed inputs, it fails to properly validate array indices or buffer boundaries, leading to memory access violations. This out-of-bounds read can result in information disclosure, system instability, or potentially allow attackers to infer memory layout details that could aid in more sophisticated exploitation techniques.
From an operational perspective, this vulnerability poses significant risks to systems that process untrusted RAR archives, particularly those running email servers, file sharing systems, or automated decompression services. Attackers could craft malicious RAR files that, when processed by vulnerable systems, trigger the out-of-bounds read condition. The impact extends beyond simple system crashes, as the memory access violations could expose sensitive data from adjacent memory regions or potentially provide information useful for privilege escalation attacks. The vulnerability is particularly concerning because RAR files are commonly used for file distribution across various platforms and applications, making the attack surface quite broad.
The exploitation of this vulnerability requires an attacker to deliver a specially crafted RAR archive that triggers the specific code path within the Unpack::Unpack20 function. This aligns with ATT&CK technique T1059.007, which covers execution through scripts, where malicious archives could be used to deliver payloads through automated decompression processes. The remediation strategy focuses on updating to UnRAR version 5.5.7 or later, which includes proper bounds checking and input validation mechanisms. Organizations should also implement network segmentation and file validation controls to prevent automatic processing of untrusted archives. Additional mitigations include deploying intrusion detection systems that can identify suspicious RAR file patterns and implementing least privilege principles for systems that handle archive decompression operations. Security teams should also consider disabling automatic decompression of RAR files in environments where the risk is high, and regularly audit systems for vulnerable software installations to ensure comprehensive protection against this and similar out-of-bounds read vulnerabilities.