Pre-auth process termination via WebSocket compression bomb
Published Feb 24, 2026 · Updated Feb 24, 2026
Denial of service in NATS Server before 2.11.12 or 2.12.0-RC.1 through 2.12.2 allows remote attackers to terminate the process. The server/websocket.go decompression path reads an entire expanded frame into memory before applying the maximum-payload check, allowing a compact frame to allocate an oversized buffer. Exploitation requires an exposed WebSocket listener with negotiated compression, but it occurs before authentication and can exhaust memory until the operating system kills the server.
Summary
What happened
Denial of service in NATS Server before 2.11.12 or 2.12.0-RC.1 through 2.12.2 allows remote attackers to terminate the process. The server/websocket.go decompression path reads an entire expanded frame into memory before applying the maximum-payload check, allowing a compact frame to allocate an oversized buffer. Exploitation requires an exposed WebSocket listener with negotiated compression, but it occurs before authentication and can exhaust memory until the operating system kills the server.
The record
- CVE
- CVE-2026-27571
- Published
- Feb 24, 2026
- Updated
- Feb 24, 2026
- Vendor
- NATS.io
- Product
- NATS Server
- Classifications
- CWE-770, CWE-409, T1499.003
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 24, 2026CVE publishedPublication date reported by the CVE source.
- Feb 24, 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=< 2.11.12
- Affected versionversion=>= 2.12.0-RC.1, < 2.12.3
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
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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