Summary
Background
NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.
When configured to accept leafnode connections (for a hub/spoke topology of multiple nats-servers), then the default configuration allows for negotiating compression; a malicious remote NATS server can trigger a server panic via that compression.
Problem Description
If the nats-server has the "leafnode" configuration enabled (not default), then anyone who can connect can crash the nats-server by triggering a panic. This happens pre-authentication and requires that compression be enabled (which it is, by default, when leafnodes are used).
Context: a NATS server can form various clustering topologies, including local clusters, and superclusters of clusters, but leafnodes allow for separate administrative domains to link together with limited data communication; eg, a server in a moving vehicle might use a local leafnode for agents to connect to, and sync up to a central service as and when available. The leafnode configuration here is where the central server allows other NATS servers to connect into it, almost like regular NATS clients. Documentation examples typically use port 7422 for leafnode communications.
Affected Versions
Version 2, prior to v2.11.14 or v2.12.5
Workarounds
Disable compression on the leafnode port:
leafnodes {
port: 7422
compression: off
}
Impact
The application dereferences a null pointer, causing a crash. Typical impact: denial of service via crash.
CVE-2026-29785 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 (2.11.14, 2.12.5); 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.
Remediation advice
github.com/nats-io/nats-server/v2 to 2.11.14 or later; github.com/nats-io/nats-server/v2 to 2.12.5 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-29785? CVE-2026-29785 is a high-severity null pointer dereference vulnerability in github.com/nats-io/nats-server/v2 (go), affecting versions < 2.11.14. It is fixed in 2.11.14, 2.12.5. The application dereferences a null pointer, causing a crash.
- How severe is CVE-2026-29785? CVE-2026-29785 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 packages are affected by CVE-2026-29785?
github.com/nats-io/nats-server/v2(go) (versions < 2.11.14)github.com/nats-io/nats-server(go) (versions > 0)
- Is there a fix for CVE-2026-29785? Yes. CVE-2026-29785 is fixed in 2.11.14, 2.12.5. Upgrade to this version or later.
- Is CVE-2026-29785 exploitable, and should I be worried? Whether CVE-2026-29785 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-2026-29785 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-2026-29785?
- Upgrade
github.com/nats-io/nats-server/v2to 2.11.14 or later - Upgrade
github.com/nats-io/nats-server/v2to 2.12.5 or later
- Upgrade