CVE-2017-7516 in cpio
Summary
by MITRE
It was found that the cpio --no-absolute-filenames option since version 2.7 did not verify paths during extraction. A specially crafted cpio archive could bypass this option and write to an arbitrary location, outside of the extraction directory.
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Analysis
by VulDB Data Team • 12/31/2019
The vulnerability identified as CVE-2017-7516 resides within the cpio archiving utility, specifically affecting versions 2.7 and later. This flaw represents a critical path traversal issue that undermines the security controls designed to prevent arbitrary file system modifications during archive extraction operations. The cpio utility, widely used in unix-like systems for creating and extracting archive files, implements a --no-absolute-filenames option intended to protect against malicious archives attempting to write files outside of the designated extraction directory. This protection mechanism fails to properly validate file paths during the extraction process, creating a significant security gap that can be exploited by attackers.
The technical flaw manifests when cpio processes archives containing specially crafted file paths that appear to be relative but are actually constructed to bypass the intended security restrictions. The vulnerability stems from inadequate input validation and path sanitization within the extraction logic, allowing attackers to manipulate the extraction behavior through carefully crafted archive contents. This weakness enables malicious actors to write files to arbitrary locations on the target system, potentially overwriting critical system files or creating backdoor access points. The flaw operates at the file system level, bypassing normal access controls and directory restrictions that should normally prevent such unauthorized modifications.
The operational impact of this vulnerability extends beyond simple privilege escalation scenarios, as it can enable attackers to compromise entire system integrity through seemingly innocuous archive extraction operations. When system administrators or automated processes extract archives without proper validation, they inadvertently create opportunities for attackers to place malicious files in critical system directories such as /bin, /etc, or other protected locations. This vulnerability particularly affects systems that routinely process untrusted archive files, including build environments, automated deployment systems, and any infrastructure that handles external archive content. The attack surface is broadened by the prevalence of cpio across various unix-like operating systems and the common practice of using archive extraction in automated workflows.
Mitigation strategies for CVE-2017-7516 should focus on immediate version updates to cpio implementations, as this vulnerability represents a fundamental flaw in path validation logic that requires core software modifications to resolve properly. Organizations should implement strict input validation procedures for all archive extraction operations, particularly in automated environments where untrusted content may be processed without manual oversight. The use of sandboxed extraction environments and privilege separation techniques can help contain potential damage from exploited archives. Additionally, system administrators should conduct thorough audits of existing systems to identify and patch vulnerable cpio versions, while implementing monitoring procedures to detect unauthorized file system modifications that might indicate exploitation attempts. This vulnerability aligns with CWE-22 Path Traversal and CWE-73 Path Traversal, and maps to ATT&CK techniques involving privilege escalation and persistence through file system manipulation. Organizations should also consider implementing automated security scanning tools that can detect and prevent the execution of potentially malicious archive content in their infrastructure.