CVE-2015-8930 in libarchive
Summary
by MITRE
bsdtar in libarchive before 3.2.0 allows remote attackers to cause a denial of service (infinite loop) via an ISO with a directory that is a member of itself.
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Analysis
by VulDB Data Team • 09/19/2022
The vulnerability identified as CVE-2015-8930 affects bsdtar, a command-line utility included in the libarchive library, which is widely used for handling various archive formats including iso9660. This flaw exists in versions prior to 3.2.0 and represents a significant security concern due to its potential for causing system instability. The vulnerability specifically manifests when bsdtar processes ISO files containing directories that reference themselves, creating a recursive loop that can consume excessive system resources and potentially lead to system crashes or unresponsiveness. The issue stems from inadequate handling of circular references within the ISO file structure, where directory entries point back to themselves in a manner that the archive extraction logic cannot properly resolve. This behavior constitutes a classic denial of service vulnerability that can be exploited by malicious actors who craft specially formatted ISO files designed to trigger the problematic code path. The vulnerability impacts systems that rely on libarchive for processing ISO images, which includes numerous operating systems and applications that utilize this library for archive handling operations.
The technical implementation of this vulnerability involves bsdtar's parsing logic failing to detect and break infinite recursion cycles when processing directory structures within ISO files. When bsdtar encounters a directory entry that references itself, the internal traversal algorithm enters an infinite loop where it continuously processes the same directory entry without proper termination conditions. This issue falls under the category of CWE-835, which specifically addresses the problem of infinite loops in software implementations, and represents a failure in proper cycle detection within data structure traversal algorithms. The flaw demonstrates poor defensive programming practices where the software does not implement adequate safeguards against circular references that could be present in malformed or maliciously crafted archive files. The implementation lacks proper state tracking mechanisms to identify when a directory has been previously encountered during traversal, resulting in the software becoming trapped in an endless processing loop that consumes CPU resources and potentially causes system instability. This behavior is particularly concerning because bsdtar is often invoked automatically by system processes or scripts during routine archive operations, making the system vulnerable to exploitation without user intervention.
The operational impact of CVE-2015-8930 extends beyond simple denial of service conditions to potentially compromise system availability and stability across multiple platforms and applications. When exploited, this vulnerability can cause systems to become unresponsive or crash entirely, particularly affecting servers or systems that process user-uploaded ISO files or automatically extract archives from untrusted sources. The vulnerability affects not only desktop systems but also server environments where automated archive processing is common, including web servers, file sharing systems, and backup applications that utilize libarchive for handling ISO images. The resource exhaustion caused by the infinite loop can lead to significant performance degradation, making the affected systems unavailable to legitimate users and potentially creating opportunities for additional attacks. Organizations that rely on automated processing of ISO files, such as software distribution platforms, cloud storage services, or enterprise backup solutions, face particular risk from this vulnerability as it can be triggered through normal operational procedures without requiring special privileges or advanced exploitation techniques. The vulnerability's impact is amplified in environments where multiple concurrent archive extractions occur, as each instance of the flaw can consume substantial system resources and potentially cause cascading failures across dependent services.
Mitigation strategies for CVE-2015-8930 primarily focus on upgrading to libarchive version 3.2.0 or later, where the issue has been addressed through improved cycle detection and handling of circular references in directory structures. System administrators should prioritize patching affected systems, particularly those that process untrusted ISO files or automatically extract archives from external sources. The upgrade process should include thorough testing to ensure that the updated libarchive library does not introduce compatibility issues with existing applications that depend on archive processing functionality. Organizations should implement additional defensive measures such as validating archive contents before processing, implementing resource limits on archive extraction operations, and monitoring for unusual CPU usage patterns that might indicate exploitation attempts. Network security controls can be enhanced by implementing file type restrictions and content filtering for ISO files, particularly in environments where users can upload or download archive files. The vulnerability highlights the importance of proper input validation and defensive programming practices in archive processing libraries, emphasizing the need for robust cycle detection mechanisms and resource management to prevent similar issues from occurring in other software components. Security teams should also consider implementing automated scanning for vulnerable systems and establishing incident response procedures specifically designed to handle denial of service attacks targeting archive processing utilities.