fix: prevent ReDoS in UriTemplate regex patterns (v1.x backport) (#1365)

Author: pcarleton

package-lock.json

@@ -1,6 +1,6 @@
 {
     "name": "@modelcontextprotocol/sdk",
-    "version": "1.25.1",
+    "version": "1.25.2",
     "description": "Model Context Protocol implementation for TypeScript",
     "license": "MIT",
     "author": "Anthropic, PBC (https://anthropic.com)",

package.json

@@ -225,7 +225,7 @@ export class UriTemplate {
 
         switch (part.operator) {
             case '':
-                pattern = part.exploded ? '([^/]+(?:,[^/]+)*)' : '([^/,]+)';
+                pattern = part.exploded ? '([^/,]+(?:,[^/,]+)*)' : '([^/,]+)';
                 break;
             case '+':
             case '#':
@@ -235,7 +235,7 @@ export class UriTemplate {
                 pattern = '\\.([^/,]+)';
                 break;
             case '/':
-                pattern = '/' + (part.exploded ? '([^/]+(?:,[^/]+)*)' : '([^/,]+)');
+                pattern = '/' + (part.exploded ? '([^/,]+(?:,[^/,]+)*)' : '([^/,]+)');
                 break;
             default:
                 pattern = '([^/]+)';

src/shared/uriTemplate.ts

@@ -284,5 +284,32 @@ describe('UriTemplate', () => {
             vars[longName] = 'value';
             expect(() => template.expand(vars)).not.toThrow();
         });
+
+        it('should not be vulnerable to ReDoS with exploded path patterns', () => {
+            // Test for ReDoS vulnerability (CVE-2026-0621)
+            // See: https://github.com/modelcontextprotocol/typescript-sdk/issues/965
+            const template = new UriTemplate('{/id*}');
+            const maliciousPayload = '/' + ','.repeat(50);
+
+            const startTime = Date.now();
+            template.match(maliciousPayload);
+            const elapsed = Date.now() - startTime;
+
+            // Should complete in under 100ms, not hang for seconds
+            expect(elapsed).toBeLessThan(100);
+        });
+
+        it('should not be vulnerable to ReDoS with exploded simple patterns', () => {
+            // Test for ReDoS vulnerability with simple exploded operator
+            const template = new UriTemplate('{id*}');
+            const maliciousPayload = ','.repeat(50);
+
+            const startTime = Date.now();
+            template.match(maliciousPayload);
+            const elapsed = Date.now() - startTime;
+
+            // Should complete in under 100ms, not hang for seconds
+            expect(elapsed).toBeLessThan(100);
+        });
     });
 });