CVE-2026-27571

5.9 MEDIUM
Published: February 24, 2026 Modified: February 26, 2026
View on NVD

Description

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.

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CVSS v3.x Details

0.0 Low Medium High Critical 10.0
Vector String
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References to Advisories, Solutions, and Tools

Patch Vendor Advisory Exploit Third Party Advisory
https://github.com/nats-io/nats-server/releases/tag/v2.11.12
Source: security-advisories@github.com
Product Release Notes
https://github.com/nats-io/nats-server/releases/tag/v2.12.3
Source: security-advisories@github.com
Product Release Notes
https://github.com/nats-io/nats-server/security/advisories/GHSA-qrvq-68c2-7grw
Source: security-advisories@github.com
Vendor Advisory

4 reference(s) from NVD

Quick Stats

CVSS v3 Score
5.9 / 10.0
EPSS (Exploit Probability)
0.1%
21th percentile
Exploitation Status
Not in CISA KEV

Weaknesses (CWE)

Affected Vendors

linuxfoundation