Executive brief
A vulnerability in the PHP programming language can allow an attacker to crash web applications or services. PHP is a widely used technology for building websites; an exploit could lead to a service outage, making a website unavailable to users. This issue specifically affects systems where PHP is running on certain operating systems like NetBSD.
Technical details
An out-of-bounds read vulnerability exists in PHP's urldecode() and other functions due to the improper handling of signed characters when passed to ctype functions like isxdigit(). In the affected versions, characters are cast to signed integers, which can result in negative values being passed to ctype functions. On platforms that use optimized table-lookups for these functions (notably NetBSD), this causes a negative array offset access. An attacker can trigger this by providing specially crafted URL-encoded strings, leading to a segmentation fault and subsequent denial of service. The issue is resolved in PHP versions 8.2.31, 8.3.31, 8.4.21, and 8.5.6.
Affected products
- PHP Group PHP 8.2.0 to 8.2.30, 8.3.0 to 8.3.30, 8.4.0 to 8.4.20, 8.5.0 to 8.5.5
Timeline
- 2026-05-07: advisory: GitHub advisory published by PHP maintainers
- 2026-05-10: disclosed: CVE published to NVD