JavaScriptCore JIT incorrect CSE leading to out-of-bounds access
CVE-2020-9802 is a JavaScriptCore/WebKit JIT compiler vulnerability affecting Apple platforms and Safari-related products. The issue was described by Apple as a logic issue in processing maliciously crafted web content that could lead to arbitrary code execution. Public technical analysis attributes the root cause to incorrect Common Subexpression Elimination (CSE) in the DFG JIT compiler: DFGClobberize did not properly account for the ArithMode of ArithNegate when modeling PureValue definitions, allowing a checked ArithNegate to be substituted with an unchecked ArithNegate. In exploitable conditions, an attacker can trigger the INT_MIN edge case in 32-bit signed arithmetic, violate compiler assumptions about integer ranges, and induce out-of-bounds read/write on the JavaScriptCore heap. Demonstrated exploitation corrupted adjacent JSArray metadata, then derived addrof and fakeobj primitives and ultimately stable arbitrary memory read/write in the Safari renderer process.
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Impact, mitigation & remediation
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Impact
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Mitigation
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Remediation
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Exploits
1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos (1 hidden).
This repository contains a browser-based exploit for CVE-2020-9802, a JIT bug in the WebKit engine affecting iOS devices. The exploit is implemented as a single HTML file ('exploit.html') containing JavaScript that manipulates memory structures to achieve arbitrary code execution. The exploit is specifically tailored for the iPod7,1 running iOS 12.5.7, using hardcoded offsets and targeting the WebKit JIT vulnerability. Upon successful exploitation, a ROP chain is executed to launch the Calculator app, demonstrating code execution outside the browser sandbox. The README provides context, credits, and references to the original research and similar implementations. No network endpoints or external domains are contacted; the exploit operates entirely within the browser context. The code is a proof-of-concept and is not weaponized for broader use.
Affected products & vendors
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Recent activity
5 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A publicly available WebKit/Safari remote code execution vulnerability used by the LightSpy operators for initial access to iOS devices.
An exploited Safari/WebKit JavaScript engine JIT vulnerability used as the basis of a renderer exploit, enabling attacker primitives such as addrof/fakeobj and leading toward arbitrary memory read/write.
A JavaScriptCore/WebKit JIT compiler vulnerability caused by incorrect Common Subexpression Elimination handling of ArithNegate/ArithMode, enabling out-of-bounds read or write on the JSC heap and browser renderer exploitation.
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Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.