Internet Bug Bounty: mb_strtolower (UTF-32LE): stack-buffer-overflow at php_unicode_tolower_full (CVE-2020-7065)

2020-04-0312:14:40

anatoliq

hackerone.com

8.8 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

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

6.8 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

PARTIAL

Availability Impact

PARTIAL

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

0.005 Low

EPSS

Percentile

72.8%

JSON

PHP bug report (made public by the maintainers at the time of writing): https://bugs.php.net/bug.php?id=79371
Mitre CVE page: https://vulners.com/cve/CVE-2020-7065
Link to the release notes: https://www.php.net/ChangeLog-7.php#7.4.4

Impact

One of impacts is that the issue allows an attacker to straightforwardly crash the PHP interpreter provided a specific UTF character can be passed to mb_strtolower function dealing with UTF-32LE encoding.

Original summary from the bug report:
> A call to mb_strtolower allows overwriting of a stack-allocated buffer with an overflown array from .rodata.

Description as provided by CVE database entry:
> In PHP versions 7.3.x below 7.3.16 and 7.4.x below 7.4.34, while using mb_strtolower() function with UTF-32LE encoding, certain invalid strings could cause PHP to overwrite stack-allocated buffer. This could lead to memory corruption, crashes and potentially code execution.