Microsoft Edge Chakra JIT BoundFunction::NewInstance Bug

2018.07.13
Risk: Medium
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: A bug in BoundFunction::NewInstance CVE-2018-8139 BoundFunction::NewInstance is used to handle calls to a bound function. The method first allocates a new argument array and copies the prepended arguments and others into the new argument array and calls the actual function. The problem is, it doesn't care about the CallFlags_NewTarget flag which indicates that there's an extra argument (new.target) at the end of the argument array. So the size of the new argument array created with the CallFlags_NewTarget flag will be always 1 less then required, this leads to an OOB read. PoC: function func() { new.target.x; } let bound = func.bind({}, 1); Reflect.construct(bound, []); This bug is subject to a 90 day disclosure deadline. After 90 days elapse or a patch has been made broadly available, the bug report will become visible to the public. Found by: lokihardt


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