(This advisory is canonically <https://advisories.nats.io/CVE/CVE-2021-32026.txt>)
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.
NATS Server:
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.
Use a configuration file to set the TLS parameters instead of command-line options.
Upgrade the NATS server.
This issue was identified and reported by SimCorp.
| Software | From | Fixed in |
|---|---|---|
github.com/nats-io/nats-server/v2
|
- | 2.2.3 |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
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