CVE-2017-9847 in libtorrent
Summary
by MITRE
The bdecode function in bdecode.cpp in libtorrent 1.1.3 allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) via a crafted file.
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Analysis
by VulDB Data Team • 12/09/2022
The vulnerability identified as CVE-2017-9847 represents a critical heap-based buffer over-read flaw within the libtorrent library version 1.1.3. This issue resides in the bdecode function implementation located in the bdecode.cpp source file, where the library fails to properly validate input data structures during torrent file parsing operations. The flaw manifests when maliciously crafted torrent files are processed by applications utilizing this version of libtorrent, creating a condition where the application attempts to read beyond the allocated heap memory boundaries. This particular vulnerability falls under the CWE-125 weakness category, which specifically addresses out-of-bounds read conditions that can lead to information disclosure, application crashes, and potential exploitation for privilege escalation attacks.
The technical exploitation of this vulnerability occurs when an attacker crafts a specially formatted torrent file containing malformed data structures that trigger improper memory access patterns within the bdecode function. During normal operation, libtorrent parses torrent files to extract metadata about the files being shared, but the flawed implementation fails to properly bounds-check the data it processes. When the bdecode function encounters the crafted input, it attempts to read memory locations that are outside the intended buffer boundaries, resulting in a heap-based buffer over-read condition. This memory corruption causes the application to crash abruptly, effectively creating a denial of service scenario that prevents legitimate users from accessing the torrent sharing functionality. The vulnerability demonstrates characteristics consistent with the ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion or application instability.
The operational impact of CVE-2017-9847 extends beyond simple application crashes to potentially compromise the availability and stability of torrent-based services and applications. Any software that relies on libtorrent 1.1.3 for peer-to-peer file sharing operations becomes vulnerable to this attack vector, including media streaming applications, file sharing platforms, and various torrent clients. The vulnerability is particularly concerning because it can be triggered remotely through the simple act of downloading or parsing a malicious torrent file, requiring no special privileges or complex attack chains. The heap-based nature of the buffer over-read means that the memory corruption can affect other data structures within the application's memory space, potentially leading to more severe consequences including information leakage or further exploitation. Organizations using affected versions of libtorrent should consider this vulnerability as a high-priority risk that could be exploited by adversaries to disrupt legitimate file sharing operations and compromise service availability.
Mitigation strategies for CVE-2017-9847 primarily focus on immediate version upgrades to libtorrent 1.1.4 or later, which contain the necessary patches to address the buffer over-read condition in the bdecode function. System administrators should implement comprehensive patch management procedures to ensure all affected applications are updated promptly, as the vulnerability can be exploited through automated means by threat actors monitoring public torrent networks. Additionally, network-level protections such as torrent file filtering and content validation can provide temporary defensive measures while updates are deployed. The vulnerability highlights the importance of proper input validation and memory safety practices in network protocols and file parsing libraries, aligning with security best practices outlined in industry standards for secure coding and vulnerability remediation. Organizations should also consider implementing monitoring solutions to detect unusual application behavior patterns that might indicate exploitation attempts, as the crash conditions can sometimes be leveraged as part of broader attack campaigns targeting peer-to-peer networks.