CVE-2025-6491: NULL Pointer Dereference in PHP SOAP Extension via Large XML Namespace Prefix

If a SoapVar instance is created with a fully qualified name larger than 2G, this will cause a NULL pointer dereference resulting in a segmentation fault, leading to a denial of service.

Libxml versions prior to 2.13 cannot correctly handle a call to xmlNodeSetName() with a name longer than 2G. It will leave the node object in an invalid state with a NULL name. This later causes a NULL pointer dereference when using the name during message serialization.

This can be exploited if a SoapVar is created with a fully qualified name that is longer than 2G. This would be possible if some application code uses a namespace prefix from an untrusted source like from a remote SOAP service.

— Red Hat

In PHP versions:8.1. before 8.1.33, 8.2. before 8.2.29, 8.3. before 8.3.23, 8.4. before 8.4.10 when parsing XML data in SOAP extensions, overly large (>2Gb) XML namespace prefix may lead to null pointer dereference. This may lead to crashes and affect the availability of the target server.

— MITRE