CVE-2017-12800 in libebml2
Summary
by MITRE
The EBML_FindNextElement function in ebmlmain.c in libebml2 through 2012-08-26 allows remote attackers to cause a denial of service (Null pointer dereference and application crash) via a crafted mkv file.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-12800 resides within the libebml2 library, specifically in the EBML_FindNextElement function located in ebmlmain.c. This library serves as a core component for handling Extensible Binary Meta Language (EBML) formatted data, which is extensively used in multimedia file formats such as Matroska (MKV). The flaw manifests when processing maliciously crafted MKV files that contain specially constructed EBML elements designed to trigger unexpected behavior in the parsing routine. This vulnerability falls under the category of a null pointer dereference, representing a classic software defect that can be exploited to disrupt service availability.
The technical exploitation of this vulnerability occurs when the EBML_FindNextElement function encounters malformed EBML elements within an MKV file that cause the function to attempt dereferencing a null pointer during element parsing operations. When the library processes these crafted inputs, the function fails to properly validate element structures, leading to a scenario where a null pointer is accessed, resulting in an application crash. This type of flaw represents a CWE-476 null pointer dereference vulnerability, which is classified as a fundamental error in pointer handling that can be systematically exploited by remote attackers without requiring special privileges. The vulnerability specifically affects libebml2 versions released through 2012-08-26, indicating a long-standing issue that was not properly addressed in the affected codebase.
The operational impact of this vulnerability extends beyond simple application instability, as it creates a reliable denial of service condition that can be triggered remotely by any user capable of providing a malicious MKV file to a vulnerable system. Attackers can construct MKV files with carefully crafted EBML structures that will cause the vulnerable application to crash whenever it attempts to parse such files, effectively rendering the application unusable for legitimate users. This type of attack aligns with ATT&CK technique T1499.004, which involves network denial of service attacks that target application availability. The vulnerability is particularly concerning in environments where applications automatically process or stream MKV content, such as media servers, content delivery networks, or media processing applications, as these systems could be reliably disrupted through simple file delivery.
Mitigation strategies for CVE-2017-12800 primarily involve upgrading to a patched version of libebml2 where the null pointer dereference has been corrected through proper input validation and error handling. System administrators should ensure that all applications utilizing libebml2 are updated to versions that address this vulnerability, particularly in environments where untrusted MKV files may be processed. Additionally, implementing proper input validation at the application level can provide defense-in-depth protection, where applications can verify MKV file integrity before processing or employ sandboxing techniques to isolate vulnerable library calls. Network-level protections such as content filtering and file type validation can also help prevent malicious MKV files from reaching vulnerable applications, while monitoring for application crashes or restarts can help detect exploitation attempts. The remediation process should include comprehensive testing of updated libraries to ensure that the fix does not introduce regressions in legitimate functionality while maintaining the required security posture against this specific denial of service vector.