CVE-2026-27571

unknown

Published 2026-02-24 · Modified 2026-03-02

💬 Discuss on Community ✚ Propose mitigation

CVSS v3

—

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

CVSS v4 NEW

—

not yet in upstream

VIR risk

—

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.

Predictions

Exploit likelihood

30%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

OS impact

OS	Version	Status	Fixed in
debian	bookworm	affected
debian	forky	fixed	`2.12.4-1`
debian	sid	fixed	`2.12.4-1`
debian	trixie	affected

Package impact

Ecosystem	Package	Vulnerable	Fixed
Go	github.com/nats-io/nats-server/v2	`<2.11.12`	`2.11.12`
Go	github.com/nats-io/nats-server/v2	`>=2.12.0-RC.1,<2.12.3`	`2.12.3`
Go	github.com/nats-io/nats-server	`<=1.4.1`
Go	github.com/nats-io/nats-server

References

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.