Internet Bug Bounty: Uninitialized read in gdImageCreateFromXbm

2019-06-2102:53:16

chamal

hackerone.com

5.3 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

LOW

Integrity Impact

NONE

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

5 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

NONE

Availability Impact

NONE

AV:N/AC:L/Au:N/C:P/I:N/A:N

0.002 Low

EPSS

Percentile

59.5%

JSON

This bug is present in gdImageCreateFromXbm method of ext/gd/libgd/gd_xbm.c file.
This method contains below mentioned lines.

...
unsigned int b;
...
sscanf(h, "%x", &b);
		for (bit = 1; bit &lt;= max_bit; bit = bit &lt;&lt; 1) {
			gdImageSetPixel(im, x++, y, (b & bit) ? 1 : 0);
...

So when sscanf method is not able to read a hex value, “b” variable will contain uninitialized data.
Bug Report : https://bugs.php.net/bug.php?id=77973
PHP Version : 7.1.29
CVE-ID : 2019-11038