Summary
(This advisory is canonically https://advisories.nats.io/CVE/CVE-2021-32026.txt)
Problem Description
The NATS server by default uses a restricted set of modern ciphersuites for TLS. This selection can be overridden through configuration. The defaults include just RSA and ECDSA with either AES/GCM with a SHA2 digest or ChaCha20/Poly1305.
The configuration system allows for extensive use of CLI options to override configuration settings. When using these to set a key/cert for TLS, the restricted ciphersuite settings were lost, enabling all ciphersuites supported by Go by default.
None of these additional ciphersuites are broken, so the NATS maintainers have fixed this in public git and the next release is not being hurried, nor is this security advisory embargoed.
Affected versions
NATS Server:
- All versions prior to 2.2.3
- fixed with nats-io/nats-server commit ffccc2e1bd (2021-04-29)
Workaround
Use a configuration file to set the TLS parameters instead of command-line options.
Credits
This issue was identified and reported by SimCorp.
Impact
If a server administrator chooses to start the nats-server with TLS configuration parameters provided on the command-line, then clients can negotiate TLS ciphersuites which were not expected.
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.
Remediation advice
Upgrade the NATS server.
Frequently Asked Questions
- What is CVE-2021-32026? CVE-2021-32026 is a low-severity security vulnerability in github.com/nats-io/nats-server/v2 (go), affecting versions < 2.2.3. It is fixed in 2.2.3.
- Which versions of github.com/nats-io/nats-server/v2 are affected by CVE-2021-32026? github.com/nats-io/nats-server/v2 (go) versions < 2.2.3 is affected.
- Is there a fix for CVE-2021-32026? Yes. CVE-2021-32026 is fixed in 2.2.3. Upgrade to this version or later.
- Is CVE-2021-32026 exploitable, and should I be worried? Whether CVE-2021-32026 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-2021-32026 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-2021-32026? Upgrade
github.com/nats-io/nats-server/v2to 2.2.3 or later.