CVE-2026-54155: High severity npm/node-opcua vulnerability
Summary A 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.
Affected versions: <= 2.165.0 Tested version: 2.165.0 CVSS Score: 8.1 (High) CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L CWE: CWE-347 Improper Verification of Cryptographic Signature
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Root Cause
In packages/node-opcua-server/source/opcuaserver.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.
This has two consequences:
1. 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.
2. Unconditional replay attack: Because nonce binding is structurally absent, any captured UserNameIdentityToken ciphertext can be replayed in a different session unconditionally.
The impact is compounded by a second issue: when the channel uses SecurityMode=None, verifyClientSignature returns true unconditionally (securitypolicy.ts:697-700), bypassing the channel-level signature check entirely.
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Proof of Concept (logic, no exploit code)
1. GetEndpoints (unauthenticated) → retrieve server public key and RSA token policy 2. OpenSecureChannel (SecurityMode=None) 3. CreateSession 4. Craft plaintext: [0x20, 0x00, 0x00, 0x00] (readUInt32LE = 32 = serverNonce.length) 5. RSA-OAEP encrypt with server public key → 256-byte ciphertext 6. ActivateSession with crafted UserNameIdentityToken 7. Server decrypts → length = 32 - 32 = 0 → password = "" 8. isValidUser(username, "") is called
Dynamically confirmed: decryption produces password = "" with no error and no nonce verification.
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Suggested Fix
After decrypting the password blob, verify that buff.slice(4 + passwordLength) equals session.nonce before extracting the password. Reject the token if verification fails.
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I 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.
Reporter: Stanley Tobias Discovery date: 2026-03-23
Affected Software
Event History
Frequently Asked Questions
Which deployments are affected?
npm/node-opcua versions up to and including 2.165.0 are affected. Version 2.165.0 was tested.
What does an attacker need to attempt the forged-password attack?
The attacker can obtain the server public key through an unauthenticated GetEndpoints request. They can then craft a UserNameIdentityToken that causes the server to validate the username with an empty password.
Which accounts are at risk from the empty-password condition?
Any account for which isValidUser accepts an empty password can be compromised through the forged token condition.
Can captured authentication tokens be reused?
Yes. Because the handler does not verify that trailing token bytes match the session nonce, captured authentication tokens can be replayed across sessions.