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BIT-nats-2026-27889 — NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead

Affected: Bitnami: nats

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.

EUVD-2026-365491

fkie_cve-2026-27889

GHSA-pq2q-rcw4-3hr6 — NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead

Affected: Go: github.com/nats-io/nats-server/v2, Go: github.com/nats-io/nats-server

### Background

NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.

When using WebSockets, a malicious client can trigger a server crash with crafted frames, before authentication.

### Problem Description

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.

### Affected versions

Version 2 from v2.2.0 onwards, prior to v2.11.14 or v2.12.5

### Workarounds

This only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If able to do so, a defense in depth of restricting either of these will mitigate the attack.

### Solution

Upgrade the NATS server to a fixed version.

### Credits

This was reported to the NATS maintainers by GitHub user Mistz1. Also independently reported by GitHub user jiayuqi7813.

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## Report by @Mistz1

### Summary

An unauthenticated remote attacker can crash the entire nats-server process by sending a single malicious WebSocket frame (15 bytes after the HTTP upgrade handshake). The server fails to validate the RFC 6455 §5.2 requirement that the most significant bit of a 64-bit extended payload length must be zero. The resulting `uint64` → `int` conversion produces a negative value, which bypasses the bounds clamp and triggers an unrecovered `panic` in the co…

RHSA-2026:21769 — Red Hat Security Advisory: Multicluster Global Hub 1.5.4 security update

grafana/tempo: Tempo: Denial of Service via large queries net/url: Incorrect parsing of IPv6 host literals in net/url crypto/x509: Incorrect enforcement of email constraints in crypto/x509 github.com/nats-io/nats-server: NATS-Server: Denial of Service via malformed WebSockets frame github.com/nats-io/nats-server: NATS-Server: Denial of Service via leafnode compression crypto/x509: crypto/tls: golang: Go: Denial of Service vulnerability in certificate chain building crypto/x509: golang: Go crypto/x509: Denial of Service via inefficient certificate chain validation golang: internal/syscall/unix: Root.Chmod can follow symlinks out of the root crypto/tls: golang: Go crypto/tls: Denial of Service via multiple TLS 1.3 key update messages github.com/buger/jsonparser: github.com/buger/jsonparser: Denial of Service via malformed JSON input github.com/jackc/pgproto3/v2: github.com/jackc/pgproto3/v2: Denial of Service via malicious PostgreSQL server google.golang.org/grpc/grpc-go: google.golang.org/grpc/authz: gRPC-Go: Authorization bypass due to improper HTTP/2 path validation nats-server: NATS-Server: Session and message hijacking via MQTT Client ID malfeasance nats-server: github.com/nats-io/nats-server: NATS-Server: Information disclosure of MQTT passwords through monitoring endpoints nats-server: github.com/nats-io/nats-server: NATS-Server: Access control bypass via unapplied ACLs in MQTT namespace nats-server: github.com/nats-io/nats-server: NATS-Server: Denial of Service via mal…

UBUNTU-CVE-2026-27889

Affected: Ubuntu:24.04:LTS: nats-server, Ubuntu:25.10: nats-server, Ubuntu:Pro:26.04:LTS: nats-server

WID-SEC-W-2026-0641 — NATS Server: Mehrere Schwachstellen ermöglichen Denial of Service

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