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CVE-2025-4919 is a critical memory corruption vulnerability in Mozilla Firefox's JavaScript engine, reported as allowing an attacker to perform out-of-bounds read or write operations on a JavaScript object by confusing array index sizes. Supporting content indicates the issue is in the IonMonkey JIT compiler, specifically in bounds-check elimination logic involving MathSpace/ExtractLinearSum and TryEliminateBoundsCheck in jit/IonAnalysis.cpp, where confusion between integer values and 32-bit wrapped values can cause incorrect elimination of bounds checks. An attacker can trigger the flaw with crafted JavaScript, including use of very large typed arrays, to obtain out-of-bounds access to adjacent memory. Affected products are Firefox before 138.0.4, Firefox ESR before 128.10.1 and 115.23.1, and Thunderbird before 128.10.2 and 138.0.2.
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A vulnerability in the IonMonkey JavaScript JIT compiler (SpiderMonkey engine) in Mozilla Firefox allows for out-of-bounds read and write via incorrect handling of MathSpace in linear sum extraction, leading to potential arbitrary code execution. The flaw was demonstrated at Pwn2Own 2025 and patched in Firefox 138.0.4.
An out-of-bounds access vulnerability in Firefox when optimizing linear sums, allowing attackers to read or write on a JavaScript object by confusing array index sizes, potentially leading to sensitive data access or code execution.
A critical out-of-bounds read/write vulnerability in Firefox's JavaScript engine due to array index confusion, demonstrated at Pwn2Own Berlin 2025.
A zero-day vulnerability in Mozilla Firefox web browser, patched in version 138.0.4 and corresponding ESR and Android versions.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.