Fixed Code injection vulnerability by using illegal function names

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Security
+- Code injection vulnerability by using illegal function names in `{function name='blah'}{/function}` 
+
 ## [3.1.38] - 2021-01-08
 
 ### Fixed

libs/sysplugins/smarty_internal_compile_function.php

@@ -58,6 +58,11 @@ class Smarty_Internal_Compile_Function extends Smarty_Internal_CompileBase
         }
         unset($_attr[ 'nocache' ]);
         $_name = trim($_attr[ 'name' ], '\'"');
+
+        if (!preg_match('/^[a-zA-Z0-9_\x80-\xff]+$/', $_name)) {
+	        $compiler->trigger_template_error("Function name contains invalid characters: {$_name}", null, true);
+        }
+
         $compiler->parent_compiler->tpl_function[ $_name ] = array();
         $save = array(
             $_attr, $compiler->parser->current_buffer, $compiler->template->compiled->has_nocache_code,

tests/UnitTests/TemplateSource/TagTests/TemplateFunction/CompileFunctionTest.php

@@ -431,5 +431,14 @@ class CompileFunctionTest extends PHPUnit_Smarty
                      array("{function name=simple}A{\$foo}\nC{/function}{call name='simple'}", "Abar\nC", 'T14', $i++),
                      array("{function name=simple}A\n{\$foo}\nC{/function}{call name='simple'}", "A\nbar\nC", 'T15', $i++),
         );
-            }
+    }
+
+    /**
+     * Test handling of function names that are a security risk
+     */
+    public function testIllegalFunctionName() {
+	    $this->expectException(SmartyCompilerException::class);
+	    $this->smarty->fetch('string:{function name=\'rce(){};echo "hi";function \'}{/function}');
+    }
+
 }