NATS: Message tracing can be redirected to arbitrary subject

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

EPSS

• CVE-2026-33249: 0.24% estimated exploitation activity in the next 30 days; percentile 14.81 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server supports telemetry on messages, using the per-message NATS headers. Problem Description A valid client which uses message tracing headers can indicate that the trace messages can be sent to an arbitrary valid subject, including those to which the client does not have publish permission. The payload is a valid trace message and not chosen by the attacker. Affected Versions Any version before v2.12.6 or v2.11.15 Workarounds None.

Published by the source

24 Mar 2026, 20:37 UTC

Last modified by the source

25 Mar 2026, 21:31 UTC

Source last checked

26 Oct 2026, 15:18 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-8m2x-3m6q-6w8j

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# Patch Next advisory brief: CVE-2026-33249

Advisory: NATS: Message tracing can be redirected to arbitrary subject
IDs: CVE-2026-33249, GHSA-8m2x-3m6q-6w8j
Record: https://patchnext.com/advisories/cve-2026-33249 (revision 1, source checked 26 Oct 2026, 15:18 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/nats-io/nats-server/v2 2.12.6, 2.11.15. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/nats-io/nats-server/v2: affected >= 2.11.0, < 2.11.15; >= 2.12.0-preview.1, < 2.12.6; fixed in 2.12.6, 2.11.15

## Suggested inspection (read-only)
- Go github.com/nats-io/nats-server/v2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/nats-io/nats-server/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8m2x-3m6q-6w8j (GitHub-reviewed advisory GHSA-8m2x-3m6q-6w8j lists affected ranges: Go github.com/nats-io/nats-server/v2 >=2.11.0 =2.12.0-preview.1 <2.12.6)

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