CVE-2020-26149 is a high-severity (CVSS 7.5) CWE-522 vulnerability in nats. A fix is available for nats — see the affected versions and patch details below.
Sensitive data exposure in NATS
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-26149 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
natsnpmnats.wsnpmDescription
Preview versions of two NPM packages and one Deno package from the NATS project contain an information disclosure flaw, leaking options to the NATS server; for one package, this includes TLS private credentials.
The _connection_ configuration options in these JavaScript-based implementations were fully serialized and sent to the server in the client's CONNECT message, immediately after TLS establishment.
The nats.js client supports Mutual TLS and the credentials for the TLS client key are included in the connection configuration options; disclosure of the client's TLS private key to the server has been observed.
Most authentication mechanisms are handled after connection, instead of as part of connection, so other authentication mechanisms are unaffected. For clarity: NATS account NKey authentication is NOT affected.
Neither the nats.ws nor the nats.deno clients support Mutual TLS: the affected versions listed below are those where the logic flaw is present. We are including the nats.ws and nats.deno versions out of an abundance of caution, as library maintainers, but rate as minimal the likelihood of applications leaking sensitive data.
Security impact:
- NPM package nats.js:
- mainline is unaffected
- beta branch is vulnerable from 2.0.0-201, fixed in 2.0.0-209
Logic flaw:
- NPM package nats.ws:
- status: preview
- flawed from 1.0.0-85, fixed in 1.0.0-111
- Deno repository https://github.com/nats-io/nats.deno
- status: preview
- flawed in all git tags prior to fix
- fixed with git tag v1.0.0-9
Impact:
For deployments using TLS client certificates (for mutual TLS), private key material for TLS is leaked from the client application to the server. If the server is untrusted (run by a third party), or if the client application also disables TLS verification (and so the true identity of the server is unverifiable) then authentication credentials are leaked.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | nats | ≥ 2.0.0-201&&< 2.0.0-209 | 2.0.0-209npm install nats@2.0.0-209 |
| 📦npm | nats.ws | ≥ 1.0.0-85&&< 1.0.0-111 | 1.0.0-111npm install nats.ws@1.0.0-111 |
Affected Products
nats.denolinuxfoundationnats.jslinuxfoundationnats.wslinuxfoundationDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nats, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nats to 2.0.0-209 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-26149 is resolved across your whole dependency graph.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.
Frequently Asked Questions
Is CVE-2020-26149 in your dependencies?
Find it across npm, including transitive dependencies.