CVE-2020-9308 in libarchive
Summary
by MITRE
archive_read_support_format_rar5.c in libarchive before 3.4.2 attempts to unpack a RAR5 file with an invalid or corrupted header (such as a header size of zero), leading to a SIGSEGV or possibly unspecified other impact.
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Analysis
by VulDB Data Team • 05/11/2025
The vulnerability identified as CVE-2020-9308 represents a critical heap-based buffer overflow condition within the libarchive library version 3.4.1 and earlier. This flaw exists in the archive_read_support_format_rar5.c component which processes RAR5 archive files, specifically when encountering malformed or corrupted headers during decompression operations. The issue manifests when the library attempts to unpack RAR5 files containing invalid header structures, particularly those with zero-sized headers, resulting in a segmentation fault that can cause application crashes or potentially enable arbitrary code execution depending on the system environment and memory layout.
The technical implementation of this vulnerability stems from insufficient input validation and boundary checking within the RAR5 format parser. When libarchive processes a RAR5 archive, it reads header information to determine the structure and contents of subsequent data blocks. However, the code fails to properly validate header sizes and offsets before attempting to allocate memory or process data segments. This lack of proper validation creates a condition where maliciously crafted RAR5 files can trigger memory corruption through invalid pointer arithmetic or buffer overreads. The vulnerability maps to CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write, both of which are classified as high-severity issues in the Common Weakness Enumeration catalog. The flaw represents a classic case of insufficient validation of input data before processing, allowing attackers to manipulate memory access patterns through crafted archive structures.
The operational impact of CVE-2020-9308 extends beyond simple application crashes to potentially enable more sophisticated attack vectors. Systems that process untrusted RAR5 archives, such as email servers, file sharing platforms, content delivery networks, and automated file processing systems, become vulnerable to denial of service attacks that can render services unavailable. The segmentation fault condition can be exploited to crash applications that utilize libarchive, leading to service disruption and potential system instability. In environments where applications are running with elevated privileges or where memory corruption could be leveraged for privilege escalation, the vulnerability may present a more serious threat. The attack surface is particularly broad since RAR5 is a widely supported archive format, and many applications across different platforms and operating systems use libarchive for archive handling operations. This vulnerability aligns with ATT&CK technique T1203 Exploitation for Client Execution, as it can be triggered through the processing of maliciously crafted files, and T1499 System Shutdown Reboot, through the potential for service disruption and system instability.
Mitigation strategies for CVE-2020-9308 should focus on immediate remediation through the upgrade to libarchive version 3.4.2 or later, which contains the necessary patches to address the buffer overflow conditions. Organizations should conduct comprehensive vulnerability assessments to identify all systems and applications that utilize libarchive, particularly those that process untrusted archive files from external sources. Network segmentation and file validation controls should be implemented to prevent automatic processing of suspicious archive files, while application-level sandboxing can provide additional protection layers. Regular security updates and patch management processes should be enforced to maintain protection against similar vulnerabilities. The fix implemented in version 3.4.2 includes enhanced input validation mechanisms that properly check header sizes and offsets before attempting to process RAR5 archive structures, preventing the exploitation of the buffer overflow condition through malformed header data. Security monitoring should be enhanced to detect unusual patterns of application crashes or memory access violations that may indicate exploitation attempts.