Summary
node-opcua: Unbounded nonce cache enables unauthenticated heap exhaustion DoS
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
Impact
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
CVE-2026-54156 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.166.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-54156? CVE-2026-54156 is a high-severity allocation of resources without limits or throttling vulnerability in node-opcua (npm), affecting versions < 2.166.0. It is fixed in 2.166.0. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- How severe is CVE-2026-54156? CVE-2026-54156 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of node-opcua are affected by CVE-2026-54156? node-opcua (npm) versions < 2.166.0 is affected.
- Is there a fix for CVE-2026-54156? Yes. CVE-2026-54156 is fixed in 2.166.0. Upgrade to this version or later.
- Is CVE-2026-54156 exploitable, and should I be worried? Whether CVE-2026-54156 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-54156 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-54156? Upgrade
node-opcuato 2.166.0 or later.