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NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead

Type: advisorySources: OSV

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server. This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-27889
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 13:59 UTC · Revision 1

Source evidence

NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead

core-osv · Original source

Published 25 Mar 2026, 19:36 UTC

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server. This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.

osv:CVE-2026-27889
Complete source record
{
  "id": "fd156d32ea8daa6d8a5dbbb9b6a2eca0066a165397f8ee1cb90cef46f0797f75",
  "url": "https://osv.dev/vulnerability/CVE-2026-27889",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead",
    "summary": "NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server. This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.",
    "evidence": "osv:CVE-2026-27889",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-27889",
      "aliases": [
        "BIT-nats-2026-27889",
        "CVE-2026-27889",
        "GHSA-pq2q-rcw4-3hr6",
        "GO-2026-4841"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
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                {
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                }
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              "database_specific": {
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                    "cpe": "cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*",
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                        "introduced": "2.2.0"
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                        "fixed": "2.11.14"
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                    "source": "CPE_RANGE"
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                  {
                    "cpe": "cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*",
                    "range": [
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                    "source": "CPE_RANGE"
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          "versions": [
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27889.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:29.318777635Z",
      "provider": "osv",
      "references": [
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27889.json",
        "https://access.redhat.com/errata/RHSA-2026:21769",
        "https://access.redhat.com/errata/RHSA-2026:22347",
        "https://access.redhat.com/errata/RHSA-2026:23345",
        "https://access.redhat.com/security/cve/CVE-2026-27889",
        "https://advisories.nats.io/CVE/secnote-2026-03.txt",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27889.json",
        "https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-27889",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2451447"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-190"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27889.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-27889",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 496109,
  "published_at": "2026-03-25T19:36:36.37+00:00"
}