PHP — CWE-407 Disclosure Brief

Project: PHP Disclosure date: 2026-03-27 Severity: HIGH Speedup: 50× Status: PATCHED

Finding

PHP's Zend engine contains two independent O(N×M) defects in named argument handling — one at compile time in zend_compile.c and one at runtime in zend_execute.c. Both perform a linear scan over M parameter names for each of N named arguments. A TODO comment in the source acknowledges the need for a hash table. Together these cause quadratic slowdown in functions with many named parameters and in hot call paths using named argument syntax.

The Defect(s)

ID	Location	Pattern	Complexity
php-0001	`Zend/zend_compile.c:3757`	`zend_get_arg_num()` scans M param names for each of N named args at compile time	O(N×M)
php-0002	`Zend/zend_execute.c:5479`	`zend_get_arg_offset_by_name()` scans M param names for each of N named args at runtime	O(N×M)

Complexity Proof

Let N = number of named arguments at a call site, M = number of parameters in the function definition.

php-0001 (compile time): zend_get_arg_num() is called once per named argument to resolve its position. Each call performs a linear scan of the function's parameter list:

For named_arg_1: scan up to M params → up to M string comparisons
For named_arg_2: scan up to M params → up to M string comparisons
...
For named_arg_N: scan up to M params → up to M string comparisons
Total: N × M comparisons per call site compiled

php-0002 (runtime): zend_get_arg_offset_by_name() is called on the hot execution path for every invocation using named argument syntax. With M = 25 params and N = 20 named args, each function call performs up to 500 string comparisons at runtime. For a function called in a loop of 100,000 iterations, that is 50 million comparisons versus 100,000 hash lookups — a 50× regression.

A HashMap<name, index> pre-built once per function definition eliminates both scans, reducing each lookup to O(1).

Impact

php-0001 affects compilation speed for PHP files with functions that have many named parameters and are called from many sites. Frameworks using named arguments extensively (Symfony, Laravel with PHP 8.0+ named arg syntax) compile slower in proportion to M×N across all call sites.

php-0002 is a runtime hot-path defect. Any PHP application using named argument syntax in performance-sensitive loops — Laravel request processing, Symfony event dispatch, high-throughput API endpoints — pays O(N×M) per call. The PHP source acknowledges this with a /* TODO: use hash table */ comment at the affected line.

The Fix

Pre-build a hash map {param_name => param_index} once when the function's op_array is finalized. Replace both zend_get_arg_num() and zend_get_arg_offset_by_name() with O(1) hash lookups against this pre-built structure.

Patch

- /* TODO: use hash table — zend_compile.c:3757 */
- int zend_get_arg_num(zend_function *fn, zend_string *name) {
-     for (uint32_t i = 0; i < fn->common.num_args; i++) {
-         if (zend_string_equals(fn->common.arg_info[i].name, name)) {
-             return (int)i;
-         }
-     }
-     return -1;
- }
+ int zend_get_arg_num(zend_function *fn, zend_string *name) {
+     if (fn->common.arg_name_map) {
+         zval *idx = zend_hash_find(fn->common.arg_name_map, name);
+         return idx ? (int)Z_LVAL_P(idx) : -1;
+     }
+     /* fallback for functions without pre-built map */
+     for (uint32_t i = 0; i < fn->common.num_args; i++) {
+         if (zend_string_equals(fn->common.arg_info[i].name, name)) {
+             return (int)i;
+         }
+     }
+     return -1;
+ }

What We Ask

Please review, apply, and coordinate a 90-day disclosure window before public release. Reply to security@undefect.com.

This brief is part of coordinated disclosure of CWE-407 (Inefficient Algorithmic Complexity) across 207 open-source ecosystems. Full report: https://undefect.com

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