[GHSA-mq36-523m-x7vv] node-opcua missing nonce verification in UserNameIdentityToken authentication

advisories/github-reviewed/2026/08/GHSA-mq36-523m-x7vv/GHSA-mq36-523m-x7vv.json

@@ -1,13 +1,13 @@
 {
   "schema_version": "1.4.0",
   "id": "GHSA-mq36-523m-x7vv",
-  "modified": "2026-08-20T18:35:33Z",
+  "modified": "2026-08-20T18:36:02Z",
   "published": "2026-08-20T18:35:33Z",
   "aliases": [
     "CVE-2026-54155"
   ],
   "summary": "node-opcua missing nonce verification in UserNameIdentityToken authentication",
-  "details": "**Summary**\nA missing nonce verification in the UserNameIdentityToken authentication handler allows an unauthenticated remote attacker to forge a password token that extracts as an empty string, and to replay captured authentication tokens across sessions.\n\n**Affected versions:** <= 2.165.0\n**Tested version:** 2.165.0\n**CVSS Score:** 8.1 (High)\n**CVSS Vector:** CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L\n**CWE:** CWE-347 Improper Verification of Cryptographic Signature\n\n---\n\n**Root Cause**\n\nIn `packages/node-opcua-server/source/opcua_server.ts` at line 1886-1887, after RSA-OAEP decrypting the UserNameIdentityToken password blob, the server reads a 4-byte little-endian length field and extracts `buff[4 : 4+length]` as the password. It never verifies that the trailing bytes equal `session.nonce`.\n\nThis has two consequences:\n\n1. **Forged empty password:** An attacker who retrieves the server's public key via an unauthenticated `GetEndpoints` call can craft a token where the 4-byte length field equals `serverNonce.length` (32). The server computes `length = 32 - 32 = 0` and calls `isValidUser(username, \"\")`. Any account that accepts an empty password is compromised.\n\n2. **Unconditional replay attack:** Because nonce binding is structurally absent, any captured UserNameIdentityToken ciphertext can be replayed in a different session unconditionally.\n\nThe impact is compounded by a second issue: when the channel uses `SecurityMode=None`, `verifyClientSignature` returns `true` unconditionally (security_policy.ts:697-700), bypassing the channel-level signature check entirely.\n\n---\n\n**Proof of Concept (logic, no exploit code)**\n\n```\n1. GetEndpoints (unauthenticated) → retrieve server public key and RSA token policy\n2. OpenSecureChannel (SecurityMode=None)\n3. CreateSession\n4. Craft plaintext: [0x20, 0x00, 0x00, 0x00]  (readUInt32LE = 32 = serverNonce.length)\n5. RSA-OAEP encrypt with server public key → 256-byte ciphertext\n6. ActivateSession with crafted UserNameIdentityToken\n7. Server decrypts → length = 32 - 32 = 0 → password = \"\"\n8. isValidUser(username, \"\") is called\n```\n\nDynamically confirmed: decryption produces `password = \"\"` with no error and no nonce verification.\n\n---\n\n**Suggested Fix**\n\nAfter decrypting the password blob, verify that `buff.slice(4 + passwordLength)` equals `session.nonce` before extracting the password. Reject the token if verification fails.\n\n---\n\nI am following a 90-day responsible disclosure policy. I am happy to provide additional technical details under embargo. Please confirm receipt at your earliest convenience.\n\nReporter: Stanley Tobias\nDiscovery date: 2026-03-23",
+  "details": "**Summary**\nA missing nonce verification in the UserNameIdentityToken authentication handler allows an unauthenticated remote attacker to forge a password token that extracts as an empty string, and to replay captured authentication tokens across sessions.\n\n**Affected versions:** < 2.166.0\n**Tested version:** 2.165.0\n**CVSS Score:** 8.1 (High)\n**CVSS Vector:** CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L\n**CWE:** CWE-347 Improper Verification of Cryptographic Signature\n\n---\n\n**Root Cause**\n\nIn `packages/node-opcua-server/source/opcua_server.ts` at line 1886-1887, after RSA-OAEP decrypting the UserNameIdentityToken password blob, the server reads a 4-byte little-endian length field and extracts `buff[4 : 4+length]` as the password. It never verifies that the trailing bytes equal `session.nonce`.\n\nThis has two consequences:\n\n1. **Forged empty password:** An attacker who retrieves the server's public key via an unauthenticated `GetEndpoints` call can craft a token where the 4-byte length field equals `serverNonce.length` (32). The server computes `length = 32 - 32 = 0` and calls `isValidUser(username, \"\")`. Any account that accepts an empty password is compromised.\n\n2. **Unconditional replay attack:** Because nonce binding is structurally absent, any captured UserNameIdentityToken ciphertext can be replayed in a different session unconditionally.\n\nThe impact is compounded by a second issue: when the channel uses `SecurityMode=None`, `verifyClientSignature` returns `true` unconditionally (security_policy.ts:697-700), bypassing the channel-level signature check entirely.\n\n---\n\n**Proof of Concept (logic, no exploit code)**\n\n```\n1. GetEndpoints (unauthenticated) → retrieve server public key and RSA token policy\n2. OpenSecureChannel (SecurityMode=None)\n3. CreateSession\n4. Craft plaintext: [0x20, 0x00, 0x00, 0x00]  (readUInt32LE = 32 = serverNonce.length)\n5. RSA-OAEP encrypt with server public key → 256-byte ciphertext\n6. ActivateSession with crafted UserNameIdentityToken\n7. Server decrypts → length = 32 - 32 = 0 → password = \"\"\n8. isValidUser(username, \"\") is called\n```\n\nDynamically confirmed: decryption produces `password = \"\"` with no error and no nonce verification.\n\n---\n\n**Suggested Fix**\n\nAfter decrypting the password blob, verify that `buff.slice(4 + passwordLength)` equals `session.nonce` before extracting the password. Reject the token if verification fails.\n\n---\n\nI am following a 90-day responsible disclosure policy. I am happy to provide additional technical details under embargo. Please confirm receipt at your earliest convenience.\n\nReporter: Stanley Tobias\nDiscovery date: 2026-03-23",
   "severity": [
     {
       "type": "CVSS_V3",
@@ -28,7 +28,7 @@
               "introduced": "0"
             },
             {
-              "last_affected": "2.165.0"
+              "fixed": "2.166.0"
             }
           ]
         }