VulnerabilityPublished 25 Mar 2026

CVE-2026-33249: nats-server · Incorrect Authorization

Affects nats-serverSource CVE Database V5

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Not known to be exploited · CVSS 4.3 Medium : upgrade to 2.12.6 or 2.11.15 when convenient.

Data as of 30 Oct 2026, 11:34 UTC

CVSS 3.1 base score

4.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 14% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.12.6, 2.11.15

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 24 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade nats-server and nats-io/nats-server to 2.12.6 or 2.11.15.

Affected software

Product	Affected	Fixed in
nats-ionats-server	Affected >=2.12.0-preview.1 <2.12.6	Fixed in 2.12.6
nats-ionats-server	Affected >=2.11.0 <2.11.15	Fixed in 2.11.15
GitHubnats-io/nats-server`pkg:github/nats-io/nats-server`Other threats	Affected >=2.11.0 <2.11.15 <2.12.6	Fixed in 2.11.15 2.12.6

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

The definitive mitigation is to upgrade nats-server to version 2.11.15 or later, or 2.12.6 or later, where the authorization checks for trace message publishing have been corrected. Since no workarounds exist, organizations should prioritize patching affected systems. Additionally, organizations should audit their messaging permissions and monitor trace message subjects for anomalies that could indicate exploitation attempts. Implementing strict network segmentation and access controls around nats-server instances can limit the ability of unauthorized clients to connect and exploit this vulnerability. Logging and alerting on unusual trace message activity can help detect attempts to misuse this flaw. Finally, reviewing client authentication and authorization policies to ensure minimal necessary privileges are granted will reduce the risk surface.

Description

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.11.0 and prior to versions 2.11.15 and 2.12.6, 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. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

Impact

The primary impact of this vulnerability is on message integrity within environments using affected nats-server versions. Unauthorized publishing of trace messages to arbitrary subjects can lead to message pollution, misleading trace data, or interference with legitimate message flows. This can degrade the reliability and trustworthiness of messaging systems, potentially causing operational disruptions or complicating incident investigations. While the payload is not attacker-controlled, the ability to send trace messages to unauthorized subjects could be exploited in multi-stage attacks or to bypass certain monitoring or filtering mechanisms. Organizations relying on nats-server for critical messaging in cloud-native or edge deployments may experience degraded service quality or increased risk of message-based attacks. Since no known exploits are currently reported in the wild, the immediate risk is moderate, but the vulnerability should be addressed promptly to prevent future exploitation.

CWE-863Incorrect Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #17OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Mar 2026, 20:45 UTC

WeaknessesCWE-863

Technical details

References

Community reviews

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