Vulnerability identifier: #VU10335

Vulnerability risk: Low

CVSSv3.1: 5.2 [CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C]

CVE-ID: CVE-2017-8923

CWE-ID: CWE-20

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
PHP
Universal components / Libraries / Scripting languages

Vendor: PHP Group

Description
The vulnerability allows a remote attacker to perform denial of service (DoS) attack.

The vulnerability exists due to insufficient input validation in zend_string_extend() function in Zend/zend_string.h when leveraging a script's use of ".=" with a long. The application does not prevent changes to string objects that can result in a negative length. A remote attacker can pass an overly long string to script, which uses ".=" operand on the supplied data and trigger application crash.

Mitigation
Update to version 5.6.31, 7.0.20 or 7.1.6.

Vulnerable software versions

PHP: 7.1.0 - 7.1.5, 7.0.0 - 7.0.19, 5.6.0 - 5.6.30, 5.5.0 - 5.5.38

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External links
http://bugs.php.net/bug.php?id=74577
http://bugs.php.net/bug.php?id=73122

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.