MQTT password disclosure via premature JWT assignment
Published Mar 25, 2026 · Updated Mar 25, 2026
Information disclosure in NATS Server before 2.11.15 or 2.12.0-RC.1 through 2.12.5 exposes MQTT passwords to remote attackers. The MQTT CONNECT parser assigns c.opts.Password to c.opts.JWT before authentication establishes that the value is a JWT, leaving the password in client options returned by monitoring. Exposure requires MQTT user/password authentication and access to the enabled monitoring port; it reveals credentials without altering messages or service availability.
Summary
What happened
Information disclosure in NATS Server before 2.11.15 or 2.12.0-RC.1 through 2.12.5 exposes MQTT passwords to remote attackers. The MQTT CONNECT parser assigns c.opts.Password to c.opts.JWT before authentication establishes that the value is a JWT, leaving the password in client options returned by monitoring. Exposure requires MQTT user/password authentication and access to the enabled monitoring port; it reveals credentials without altering messages or service availability.
The record
- CVE
- CVE-2026-33216
- Published
- Mar 25, 2026
- Updated
- Mar 25, 2026
- Vendor
- NATS.io
- Product
- NATS Server
- Classifications
- CWE-213, CWE-256, T1552
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 25, 2026CVE publishedPublication date reported by the CVE source.
- Mar 25, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 2.11.15
- Affected versionversion=>= 2.12.0-RC.1, < 2.12.6
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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