CVE-2017-8923

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 7.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2017-05-12 · updated 2026-06-17
Weakness: CWE-787

Description

The zend_string_extend function in Zend/zend_string.h in PHP through 7.1.5 does not prevent changes to string objects that result in a negative length, which allows remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact by leveraging a script's use of .= with a long string.

Affected products

PHP: before 7.4.24; from 8.0.0 before 8.0.11 — fixed in 7.4.24, 8.0.11

How to fix

Upgrade to a fixed version: PHP 7.4.24, 8.0.11. Check the vendor advisory for mitigations.

References

http://www.securityfocus.com/bid/98518
https://bugs.php.net/bug.php?id=74577
http://www.securityfocus.com/bid/98518
https://bugs.php.net/bug.php?id=74577
https://security.netapp.com/advisory/ntap-20241227-0007/

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