CVE-2018-5094 in Firefox
Summary
by MITRE
A heap buffer overflow vulnerability may occur in WebAssembly when "shrinkElements" is called followed by garbage collection on memory that is now uninitialized. This results in a potentially exploitable crash. This vulnerability affects Firefox < 58.
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Analysis
by VulDB Data Team • 12/30/2019
The heap buffer overflow vulnerability identified as CVE-2018-5094 represents a critical memory safety issue within the Firefox web browser's WebAssembly implementation. This vulnerability manifests when the WebAssembly engine processes certain memory operations that involve the shrinkElements function followed by garbage collection cycles on previously uninitialized memory regions. The flaw occurs at the intersection of WebAssembly's memory management mechanisms and Firefox's garbage collection system, creating a scenario where memory boundaries are not properly validated during the shrinking process. The vulnerability specifically affects Firefox versions prior to 58, indicating that this was a targeted issue within the browser's WebAssembly execution environment that required specific conditions to be exploited.
The technical implementation of this vulnerability stems from improper handling of memory allocation and deallocation sequences within the WebAssembly runtime. When shrinkElements is invoked on WebAssembly memory, it attempts to reduce the size of allocated memory blocks, but fails to properly account for memory that has already been marked for garbage collection. The garbage collection process subsequently accesses memory regions that have been partially deallocated or uninitialized, leading to a buffer overflow condition. This type of vulnerability falls under CWE-121, heap-based buffer overflow, where the overflow occurs in heap memory rather than stack memory, making it particularly challenging to detect and exploit. The vulnerability demonstrates a classic memory safety issue where the application fails to maintain proper bounds checking during dynamic memory operations.
The operational impact of CVE-2018-5094 extends beyond simple crash conditions to potentially enable remote code execution in carefully crafted attack scenarios. When exploited, this vulnerability can cause Firefox to crash unpredictably, potentially allowing attackers to execute arbitrary code with the privileges of the browser process. The attack surface is primarily through malicious WebAssembly code delivered via web pages, where attackers can construct specific memory manipulation sequences that trigger the vulnerable code path. This vulnerability aligns with ATT&CK technique T1059.007 for WebAssembly-based attacks and represents a sophisticated vector for browser exploitation. The timing of the vulnerability's exploitation is critical, as it requires specific sequence of operations that must be carefully orchestrated to achieve reliable exploitation. The crash behavior makes this vulnerability particularly dangerous as it can be used to perform denial-of-service attacks or as a stepping stone for more complex exploitation techniques.
Mitigation strategies for CVE-2018-5094 primarily focus on upgrading to Firefox version 58 or later, where the vulnerability has been patched through improved memory management and bounds checking mechanisms. Security researchers recommend implementing additional browser hardening measures such as address space layout randomization and stack canaries to reduce exploit reliability. The patch addresses the core issue by ensuring proper memory validation during shrinkElements operations and implementing stricter garbage collection protocols that prevent access to uninitialized memory regions. Organizations should also consider implementing web application firewalls and content security policies to limit exposure to malicious WebAssembly content. The vulnerability highlights the importance of comprehensive memory safety testing in modern browser engines and underscores the need for continuous security auditing of complex runtime environments like WebAssembly implementations. Regular security updates and patch management programs are essential to protect against similar memory safety vulnerabilities that may exist in other browser components or third-party libraries.