tls: fix case-sensitive SNI context matching

mcollina · aduh95 · commit 31beb4f70784 · 2026-06-17T20:02:06.000+02:00
The regex constructed by server.addContext() lacked the case-insensitive flag, causing uppercase or mixed-case SNI hostnames from ClientHello to miss their intended context and fall back to the default context. This violates RFC 6066 Section 3, which states that DNS hostnames are case-insensitive. In mTLS configurations with per-tenant contexts, this allowed bypassing client certificate authorization by simply uppercasing the SNI hostname. Add the 'i' flag to the RegExp in addContext() so that SNI matching is case-insensitive. PR-URL: nodejs-private/node-private#857 Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com> CVE-ID: CVE-2026-48928 Refs: https://hackerone.com/reports/3656869
diff --git a/lib/internal/tls/wrap.js b/lib/internal/tls/wrap.js
@@ -1572,7 +1572,7 @@ Server.prototype.addContext = function(servername, context) {
     servername
       .replace(/([.^$+?\-\\[\]{}])/g, '\\$1')
       .replaceAll('*', '[^.]*')
-  }$`);
+  }$`, 'i');
 
   const secureContext =
     context instanceof common.SecureContext ? context : tls.createSecureContext(context);
diff --git a/test/parallel/test-tls-sni-case-insensitive.js b/test/parallel/test-tls-sni-case-insensitive.js
@@ -0,0 +1,79 @@
+'use strict';
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+// Test that SNI context matching is case-insensitive, as required by
+// RFC 6066 Section 3 and RFC 6125. Uppercase SNI hostnames must select
+// the same context as their lowercase equivalents.
+
+const assert = require('assert');
+const tls = require('tls');
+const fixtures = require('../common/fixtures');
+
+function loadPEM(n) {
+  return fixtures.readKey(`${n}.pem`);
+}
+
+const serverOptions = {
+  key: loadPEM('agent2-key'),
+  cert: loadPEM('agent2-cert'),
+};
+
+const SNIContexts = {
+  'a.example.com': {
+    key: loadPEM('agent1-key'),
+    cert: loadPEM('agent1-cert'),
+  },
+  '*.test.com': {
+    key: loadPEM('agent3-key'),
+    cert: loadPEM('agent3-cert'),
+  },
+};
+
+const tests = [
+  // Exact match, uppercase
+  { servername: 'A.EXAMPLE.COM', expectedCert: 'agent1', desc: 'uppercase exact' },
+  // Mixed case
+  { servername: 'A.Example.Com', expectedCert: 'agent1', desc: 'mixed case exact' },
+  // Wildcard match, uppercase
+  { servername: 'B.TEST.COM', expectedCert: 'agent3', desc: 'uppercase wildcard' },
+  // Wildcard match, mixed case
+  { servername: 'b.Test.Com', expectedCert: 'agent3', desc: 'mixed case wildcard' },
+  // Lowercase still works
+  { servername: 'a.example.com', expectedCert: 'agent1', desc: 'lowercase exact' },
+];
+
+let remaining = tests.length;
+
+for (const { servername, expectedCert, desc } of tests) {
+  const server = tls.createServer(serverOptions, common.mustCall((c) => {
+    // The server should have selected the correct SNI context regardless of case
+    const cert = c.getCertificate();
+    assert.strictEqual(
+      cert.subject.CN, expectedCert,
+      `${desc}: expected server cert CN=${expectedCert}, got ${cert.subject.CN}`
+    );
+    c.end();
+  }));
+
+  server.addContext('a.example.com', SNIContexts['a.example.com']);
+  server.addContext('*.test.com', SNIContexts['*.test.com']);
+
+  server.listen(0, common.mustCall(() => {
+    const client = tls.connect({
+      port: server.address().port,
+      servername,
+      rejectUnauthorized: false,
+    }, common.mustCall(() => {
+      client.end();
+    }));
+
+    client.on('close', common.mustCall(() => {
+      server.close();
+      if (--remaining === 0) {
+        process.stdout.write('all tests passed\n');
+      }
+    }));
+  }));
+}
