CVE-2026-27571

highpriority · track · 30EPSS 0.005 · 45 %ileDEEUUS
grimoire priorityP2 · Scheduled
Exploitable?
—
no known exploitation
Likely / severe?
0.54% (45th) EPSS
CVSS 7.5 · high
Is it mine?
14 products
Check your exposure
Who says so?
5 sources
cnnvd · enisa_euvd · osv · cert_bund

EPSS · scored 2026-10-27

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.

01

cvss

Technical severity, 0–10. One row per scoring source.

7.5
010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 5.9–7.5

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 3.6
v3.15.9mediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · ENISA EU
v3.15.9mediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · security-advisories@github.comexploitability 2.2 · impact 3.6
v3.15.9mediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · OSV
v3.16.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:Usecondary · CVSS-BT (t0sche)
02

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Trackcoordinatorcisa_ssvcUS
03

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-409USCWE-409USCWE-770USCWE-770US
04

affected products (14)

Products and version ranges known to be affected.

05

advisories (4)

Vendor and ecosystem advisories describing this.

  • WID-SEC-W-2026-0487NATS Server: Schwachstelle ermöglicht Denial of ServiceDeutsch2026-02-23csaf · cert_bundDE

    Ein entfernter, anonymer Angreifer kann eine Schwachstelle in NATS Server ausnutzen, um einen Denial of Service Angriff durchzuführen.

  • GHSA-qrvq-68c2-7grwnats-server websockets are vulnerable to pre-auth memory DoS2026-02-24ghsa · osvUS

    ### Impact The WebSockets handling of NATS messages handles compressed messages via the WebSockets negotiated compression. 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 was to bounds the decompression to fail once the message was too large, instead of continuing on. ### Patches This was released in nats-server without being highlighted as a security issue. It should have been, this was an oversight. Per the NATS security policy, because this does not require a valid user, it is CVE-worthy. This was fixed in the v2.11 series with v2.11.12 and in the v2.12 series with v2.12.3. ### Workarounds This only affects deployments which use WebSockets and which expose the network port to untrusted end-points. ### References This was reported to the NATS maintainers by Pavel Kohout of Aisle Research (www.aisle.com).

  • BIT-nats-2026-27571nats-server websockets are vulnerable to pre-auth memory DoS2026-03-02vendor · osvUS

    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.

  • GO-2026-4533nats-server websockets are vulnerable to pre-auth memory DoS in github.com/nats-io/nats-server2026-02-25vendor · osvUS

    nats-server websockets are vulnerable to pre-auth memory DoS in github.com/nats-io/nats-server

06

also known as (6)

Other names and identifiers for this entity.

07

sources

Which sources assert this record, and when.

cnnvdenisa_euvdosvcert_bundnvdNVDCVE.orgMITRE
published 2026-02-24modified 2026-06-17
08

references (13)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan