CVE-2018-6548 in libwebm
Summary
by MITRE
A use-after-free issue was discovered in libwebm through 2018-02-02. If a Vp9HeaderParser was initialized once before, its property frame_ would not be changed because of code in vp9parser::Vp9HeaderParser::SetFrame. Its frame_ could be freed while the corresponding pointer would not be updated, leading to a dangling pointer. This is related to the function OutputCluster in webm_info.cc.
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Analysis
by VulDB Data Team • 01/01/2020
The vulnerability identified as CVE-2018-6548 represents a critical use-after-free flaw within the libwebm library, a component widely utilized for processing webm multimedia files. This issue specifically affects versions of libwebm released through February 2, 2018, creating a persistent security risk for applications that depend on this library for media processing operations. The flaw manifests in the Vp9HeaderParser class where improper memory management leads to the creation of dangling pointers that can be exploited by malicious actors. The vulnerability stems from the Vp9HeaderParser's initialization process and subsequent handling of the frame_ property within the SetFrame function, which fails to properly update pointer references when memory is deallocated.
The technical implementation of this vulnerability involves a fundamental memory management error where the frame_ property of the Vp9HeaderParser class becomes disconnected from its actual memory allocation. When the parser is initialized and subsequently encounters certain processing conditions, the memory allocated to frame_ gets freed but the pointer reference remains unchanged, creating a dangling pointer situation. This condition is particularly dangerous because it allows for potential code execution or memory corruption when the application attempts to access the freed memory location. The issue is further compounded by the function OutputCluster in webm_info.cc which serves as the entry point where the problematic memory state is exploited, making it a critical point of failure in the library's processing pipeline.
The operational impact of CVE-2018-6548 extends beyond simple memory corruption, potentially enabling remote code execution in applications that process untrusted webm files through the affected libwebm library. This vulnerability can be exploited by attackers who craft malicious webm files designed to trigger the specific memory management conditions that lead to the use-after-free state. The attack surface is significant given that libwebm is used across various media processing applications, browsers, and multimedia frameworks that handle webm content. Security researchers have classified this as a high-severity vulnerability under CWE-416, which specifically addresses use-after-free conditions in software applications. The vulnerability aligns with ATT&CK technique T1059.007, where adversaries leverage memory corruption vulnerabilities to execute malicious code through compromised applications.
Mitigation strategies for CVE-2018-6548 require immediate updates to the libwebm library to versions that address the memory management flaw in Vp9HeaderParser. Organizations should implement comprehensive patch management protocols to ensure all affected applications are updated with the corrected library versions. Additionally, input validation and sanitization measures should be strengthened to prevent processing of untrusted webm files until the vulnerability is fully addressed. The fix typically involves proper pointer management within the SetFrame function and ensuring that the frame_ property is correctly updated when memory is reallocated or deallocated. Security teams should also consider implementing runtime monitoring and anomaly detection systems to identify potential exploitation attempts targeting this specific vulnerability pattern.