Nats Server
CVE-2026-27571
MEDIUM
GHSA-qrvq-68c2-7grw
Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
3DescriptionGitHub Advisory
NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. The WebSockets handling of NATS messages handles compressed messages via the WebSockets negotiated compression. Prior to versions 2.11.2 and 2.12.3, the implementation bound the memory size of a NATS message but did not independently bound the memory consumption of the memory stream when constructing a NATS message which might then fail validation for size reasons. An attacker can use a compression bomb to cause excessive memory consumption, often resulting in the operating system terminating the server process. The use of compression is negotiated before authentication, so this does not require valid NATS credentials to exploit. The fix, present in versions 2.11.2 and 2.12.3, was to bounds the decompression to fail once the message was too large, instead of continuing on. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points.
AnalysisAI
NATS Server versions prior to 2.11.2 and 2.12.3 fail to properly limit memory allocation during WebSocket compression, allowing unauthenticated attackers to trigger denial of service through compression bomb attacks that exhaust server memory. The vulnerability is exploitable pre-authentication since compression negotiation occurs before credential validation. A patch is available in versions 2.11.2 and 2.12.3.
Technical ContextAI
Affects Nats-Server. NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. The WebSockets handling of NATS messages handles compressed messages via the WebSockets negotiated compression. Prior to versions 2.11.2 and 2.12.3, the implementation bound the memory size of a NATS message but did not independently bound the memory consumption of the memory stream when constructing a NATS message which might then fail validation for size reasons. An attacker can use a compression bo
RemediationAI
A vendor patch is available — apply it immediately. Restrict network access to the affected service where possible.
More in Nats Server
View allNATS Server 2.x before 2.2.0 and JWT library before 2.0.1 have Incorrect Access Control because Import Token bindings ar
The JWT library in NATS nats-server before 2.1.9 has Incorrect Access Control because of how expired credentials are han
This affects all versions of package github.com/nats-io/nats-server/server. Rated high severity (CVSS 7.5), this vulnera
NATS nats-server before 2.7.2 has Incorrect Access Control. Rated high severity (CVSS 8.8), this vulnerability is remote
Authentication bypass in NATS Server (nats-io/nats-server) lets an unauthenticated attacker on an adjacent network conne
Remote denial of service in the NATS Server (nats-io/nats-server) leafnode subsystem allows unauthenticated attackers to
Denial of service in NATS Server (nats-server) MQTT handler allows a remote, unauthenticated client to exhaust server me
An integer overflow in NATS Server before 2.0.2 allows a remote attacker to crash the server by sending a crafted reques
Remote denial-of-service in NATS Server (nats-server) affects deployments with the WebSocket listener enabled but MQTT d
NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise,
The JWT library in NATS nats-server before 2.1.9 allows a denial of service (a nil dereference in Go code). Rated high s
Protocol injection in NATS Server MQTT support allows an authenticated MQTT client to smuggle control characters (tab, n
Same technique Information Disclosure
View allVendor StatusVendor
SUSE
Severity: Medium| Product | Status |
|---|---|
| openSUSE Leap 15.6 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Fixed |
| openSUSE Leap 15.5 | Fixed |
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External POC / Exploit Code
Leaving vuln.today