**Summary** A process-global nonce cache with no eviction policy allows an unauthenticated remote attacker to exhaust server heap memory by repeatedly opening sessions, causing the node-opcua server process to crash. **Affected versions:** <= 2.165.0 **Tested version:** 2.165.0 **CVSS Score:** 7.5 (High) **CVSS Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H **CWE:** CWE-770 Allocation of Resources Without Limits or Throttling --- **Root Cause** In `packages/node-opcua-secure-channel/source/server/server_secure_channel_layer.ts` at line 156, `g_alreadyUsedNonce` is a process-global object used to track previously seen nonces for replay detection. Entries are added on every `OpenSecureChannelRequest` and every `CreateSession` request but are never removed or expired. An unauthenticated attacker can exploit the `CreateSession` path (which requires no certificate) to accumulate nonce entries indefinitely. Even with `maxSessions=10` limiting concurrent sessions, nonces persist after session expiry, allowing slow but reliable heap exhaustion across repeated connection cycles. --- **Measured Impact** Dynamically confirmed heap growth: - 5,000 unique nonces → +1.23 MB resident heap, no eviction after explicit GC - Projected: 10^6 nonces → ~246 MB resident heap - Achievable OOM on default Node.js heap limits --- **Suggested Fix** Add a TTL-based eviction policy to `g_alreadyUsedNonce`. Nonces should be expired after the maximum session timeout (or a reasonable fixed window, e.g. 1 hour). A Map with timestamp entries and periodic cleanup is sufficient. --- 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