How severe is CVE-2026-33223?

CVE-2026-33223 has a CVSS score of 6.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-33223?

CVE-2026-33223 affects the following packages: github.com/nats-io/nats-server/v2 (Go), github.com/nats-io/nats-server/v2 (Go), github.com/nats-io/nats-server (Go). Ecosystems affected: Go.

How do I fix CVE-2026-33223?

Update github.com/nats-io/nats-server/v2 to 2.11.15 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33223 is resolved across your whole dependency graph.

How do I detect CVE-2026-33223 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/nats-io/nats-server/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-33223 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-33223 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-33223 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-33223?

CVE-2026-33223 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 12th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-33223?

CVE-2026-33223 is classified as CWE-290 (CWE-290). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-33223 published, and has it been updated?

CVE-2026-33223 was published on March 25, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2026-33223 — nats-server

MEDIUM

CVE-2026-33223 is a medium-severity (CVSS 6.4) CWE-290 vulnerability in github.com/nats-io/nats-server/v2. A fix is available for github.com/nats-io/nats-server/v2 — see the affected versions and patch details below.

NATS Server: Incomplete Stripping of Nats-Request-Info Header Allows Identity Spoofing

Also known asBIT-nats-2026-33223GHSA-pwx7-fx9r-hr4hGO-2026-4835

Published

Mar 25, 2026

Updated

Oct 28, 2026

Affected

3 pkgs

Patched

2 / 3

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33223.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs12th percentile — riskier than 12% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

3 pkgs affected

🐹github.com/nats-io/nats-server/v2🐹github.com/nats-io/nats-server/v2🐹github.com/nats-io/nats-server

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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 offers a Nats-Request-Info: message header, providing information about a request.

Problem Description

The NATS message header Nats-Request-Info: is supposed to be a guarantee of identity by the NATS server, but the stripping of this header from inbound messages was not fully effective.

An attacker with valid credentials for any regular client interface could thus spoof their identity to services which rely upon this header.

Affected Versions

Any version before v2.12.6 or v2.11.15

Workarounds

None.

Affected Packages

3 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/nats-io/nats-server/v2`	all versions	2.11.15`go get github.com/nats-io/nats-server/v2@v2.11.15`
🐹Go	`github.com/nats-io/nats-server/v2`	≥ 2.12.0-RC.1&&< 2.12.6	2.12.6`go get github.com/nats-io/nats-server/v2@v2.12.6`
🐹Go	`github.com/nats-io/nats-server`	all versions	No fix

Affected Products

1 product · 2 configurations

Application

nats-serverlinuxfoundation

≥ 2.12.0 && < 2.12.6

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/nats-io/nats-server/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/nats-io/nats-server/v2 to 2.11.15 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33223 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-33223 (CC BY 4.0)

Frequently Asked Questions

### 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 offers a `Nats-Request-Info:` message header, providing information about a request. ### Problem Description The NATS message header `Nats-Request-Info:` is supposed to be a guarantee of identity by the NATS server, but the stripping of this header from inbound messages was not fully effective. An attacker with valid credentials for any regular client interface could thus spoof their identity to services which rely