CVE-2020-26952 in Firefox
Summary
by MITRE • 12/09/2020
Incorrect bookkeeping of functions inlined during JIT compilation could have led to memory corruption and a potentially exploitable crash when handling out-of-memory errors. This vulnerability affects Firefox < 83.
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Analysis
by VulDB Data Team • 02/09/2026
The vulnerability identified as CVE-2020-26952 represents a critical memory corruption flaw within the JavaScript engine of Mozilla Firefox browsers. This issue stems from improper tracking of function inlining operations that occur during just-in-time compilation processes. The flaw manifests specifically when the browser encounters out-of-memory conditions, creating a scenario where memory management becomes compromised. The vulnerability affects all versions of Firefox prior to version 83, making it a widespread concern for users running older browser versions.
The technical root cause of this vulnerability lies in the incorrect bookkeeping mechanisms employed by the JavaScript engine's JIT compiler. During the compilation process, functions are inlined to optimize performance, but the system fails to properly maintain accurate records of these inlined functions. When memory allocation fails and the system attempts to handle out-of-memory errors, this corrupted bookkeeping leads to memory corruption. The flaw occurs at the intersection of compiler optimization and memory management, where the inlining state becomes inconsistent with actual memory layout. This misalignment creates opportunities for memory corruption that can potentially be exploited by malicious actors.
The operational impact of this vulnerability extends beyond simple browser instability, presenting a significant security risk that could enable remote code execution. When an attacker can trigger the specific conditions that lead to this memory corruption, they may be able to manipulate the browser's memory layout to execute arbitrary code. The vulnerability's exploitability is enhanced by the fact that it occurs during error handling scenarios, which are often less scrutinized than normal execution paths. This makes it particularly dangerous as legitimate browser operations can inadvertently trigger the exploitable condition. The memory corruption can manifest in various ways including heap corruption, stack corruption, or other memory layout issues that compromise the browser's security boundaries.
This vulnerability maps to CWE-122, which describes improper restriction of operations within a memory buffer, and aligns with ATT&CK technique T1059.007 for JavaScript-based execution. The flaw demonstrates how JIT compiler optimizations can introduce security vulnerabilities when proper memory management is not maintained throughout the entire compilation lifecycle. Organizations should prioritize immediate patching of affected Firefox versions to prevent exploitation, as the vulnerability represents a direct threat to browser security. The remediation process involves updating to Firefox version 83 or later, where the memory bookkeeping mechanisms have been corrected to properly track inlined functions during JIT compilation. Security teams should also monitor for any exploitation attempts targeting this specific vulnerability, as it represents a well-documented attack vector that may be actively targeted in the wild.