CVE-2017-12801 in libEBML
Summary
by MITRE
The UpdateDataSize function in ebmlmaster.c in libebml2 through 2012-08-26 allows remote attackers to cause a denial of service (assert fault) via a crafted mkv file.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-12801 resides within the libebml2 library, specifically in the UpdateDataSize function located in ebmlmaster.c. This library serves as a foundational component for processing EBML (Extensible Binary Meta Language) formatted files, which are commonly used in multimedia applications, particularly in the Matroska container format known as mkv files. The flaw manifests when the library processes malformed or crafted mkv files that contain specially constructed data structures designed to exploit the function's handling of data size calculations. The vulnerability is classified as a denial of service condition that occurs through an assertion failure, indicating that the software encounters an unexpected state that triggers an internal assertion check, causing the application to terminate abruptly.
The technical implementation of this vulnerability stems from inadequate input validation within the UpdateDataSize function. When processing a maliciously crafted mkv file, the function fails to properly validate the size parameters of embedded elements, leading to a scenario where an assertion condition becomes false. This assertion failure represents a fundamental breakdown in the library's error handling mechanisms, as it does not gracefully manage malformed input data. The vulnerability operates at the binary parsing level where the library attempts to calculate and update data sizes for EBML elements, and when confronted with unexpected or malformed size values, the assertion mechanism triggers a program termination rather than allowing the application to continue processing or gracefully handle the error.
The operational impact of this vulnerability extends beyond simple service disruption, as it creates a potential vector for attackers to remotely compromise systems that rely on libebml2 for processing multimedia content. Any application or service that utilizes this library to parse mkv files becomes susceptible to this denial of service attack, including media players, streaming servers, and content management systems. The remote nature of the attack means that an attacker can exploit this vulnerability without requiring local access to the target system, making it particularly dangerous in networked environments where multimedia files are frequently processed. The assertion fault results in immediate application termination, effectively denying legitimate users access to the service while potentially exposing the system to further exploitation attempts.
Mitigation strategies for this vulnerability require immediate patching of affected systems, as the most effective solution involves updating to a version of libebml2 that contains fixed implementations of the UpdateDataSize function. Organizations should prioritize updating their software stacks to versions that address this specific assertion failure and implement proper input validation mechanisms. Additionally, deployment of defensive measures such as input sanitization layers and file format validation can help reduce the risk of exploitation, though these approaches are less effective than proper patching. The vulnerability aligns with CWE-617, which addresses reachable assertions, and represents a clear violation of secure coding practices that emphasize robust error handling and input validation. From an ATT&CK perspective, this vulnerability maps to the T1499.004 technique related to network denial of service attacks, where adversaries leverage software flaws to disrupt legitimate services. Organizations should also consider implementing network segmentation and monitoring for unusual application termination patterns that may indicate exploitation attempts, as the assertion failure creates detectable behavioral anomalies in affected systems.