CVE-2017-20006 in UnRAR
Summary
by MITRE • 07/01/2021
UnRAR 5.6.1.2 and 5.6.1.3 has a heap-based buffer overflow in Unpack::CopyString (called from Unpack::Unpack5 and CmdExtract::ExtractCurrentFile).
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Analysis
by VulDB Data Team • 08/11/2025
The vulnerability identified as CVE-2017-20006 represents a critical heap-based buffer overflow within the UnRAR library version 5.6.1.2 and 5.6.1.3. This flaw exists in the Unpack::CopyString function which is invoked by both Unpack::Unpack5 and CmdExtract::ExtractCurrentFile components of the decompression engine. The issue arises when processing specially crafted archive files that contain malformed data structures, particularly within RAR archives that utilize the RAR5 compression format. The vulnerability manifests during the extraction process when the library attempts to copy string data from compressed archives to heap memory locations without proper bounds checking, creating a condition where attacker-controlled input can overwrite adjacent memory regions.
The technical implementation of this buffer overflow stems from inadequate input validation within the decompression routines of the UnRAR library. When the Unpack::CopyString function processes data from RAR5 archives, it fails to properly verify the length of string data being copied, allowing maliciously constructed archive entries to exceed allocated buffer boundaries. This vulnerability falls under CWE-121 Heap-based Buffer Overflow, which specifically addresses buffer overflows occurring in heap memory regions where data is dynamically allocated and managed. The flaw demonstrates characteristics consistent with CWE-787 Out-of-bounds Write, as the overflow occurs when attempting to write data beyond the bounds of a heap-allocated buffer. The attack vector requires an adversary to craft a malicious RAR archive file that, when processed by an application using the vulnerable UnRAR library, triggers the exploitable code path.
The operational impact of CVE-2017-20006 extends significantly across various software ecosystems that rely on UnRAR for archive handling capabilities. Applications including web browsers, email clients, file managers, and security scanning tools that incorporate the affected UnRAR library versions are vulnerable to remote code execution when processing untrusted RAR archives. This vulnerability can be exploited through multiple attack vectors as outlined in the MITRE ATT&CK framework under T1059 Command and Scripting Interpreter and T1203 Exploitation for Client Execution. The vulnerability is particularly concerning because it can be triggered through automated processes such as email attachment processing, web-based file downloads, or automated archive extraction in security tools. The heap corruption resulting from this overflow can lead to arbitrary code execution, denial of service conditions, or information disclosure depending on the specific memory layout and exploitation techniques employed by attackers.
Mitigation strategies for CVE-2017-20006 primarily focus on immediate remediation through library version updates, as the vulnerability has been addressed in subsequent releases of the UnRAR library. Organizations should prioritize updating all systems and applications that utilize the vulnerable library versions to the patched releases. Additionally, implementing input validation controls and sandboxing mechanisms can provide defense-in-depth measures against exploitation attempts. Network administrators should consider implementing content filtering solutions that scan archive files for known malicious patterns or employ heuristic analysis to identify potentially harmful archive structures. Security monitoring should include detection of unusual archive processing activities that may indicate exploitation attempts, while application developers should ensure proper bounds checking in their own code when interacting with the UnRAR library. The vulnerability demonstrates the importance of proper memory management practices and input validation in security-critical components, aligning with security standards such as those outlined in the OWASP Top Ten and NIST Special Publication 800-125 for secure software development practices.