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 …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server supports telemetry on messages, using the per-message NATS headers. Problem Description A valid client which uses message tracing headers can indicate that the trace messages can be sent to an arbitrary valid subject, including those to which the client does not have publish permission. The payload is …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server allows hub/spoke topologies using "leafnode" connections by other nats-servers. NATS messages can have headers. Problem Description The nats-server offers a Nats-Request-Info: message header, providing information about a request. This is supposed to provide enough information to allow for account/user identification, such that NATS clients could make their …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server offers a Nats-Request-Info: message header, providing information about a request. Problem Description The NATS message header Nats-Request-Info: is supposed to be a guarantee of identity by the NATS server, but the stripping of this header from inbound messages was not fully effective. An attacker with valid credentials …
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 configured to accept leafnode connections (for a hub/spoke topology of multiple nats-servers), then the default configuration allows for negotiating compression; a malicious remote NATS server can trigger a server panic via that compression. Problem Description If the nats-server has the "leafnode" configuration enabled (not default), then anyone who …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The persistent storage feature, JetStream, has a management API which has many features, amongst which are backup and restore. Problem Description Users with JetStream admin API access to restore one stream could restore to other stream names, impacting data which should have been protected against them. Affected Versions Any …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server provides an MQTT client interface. Problem Description Sessions and Messages can by hijacked via MQTT Client ID malfeasance. Affected Versions Any version before v2.12.6 or v2.11.15 Workarounds None. Resources This document is canonically: https://advisories.nats.io/CVE/secnote-2026-06.txt GHSA advisory: https://github.com/nats-io/nats-server/security/advisories/GHSA-fcjp-h8cc-6879 MITRE CVE entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33215
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server allows hub/spoke topologies using "leafnode" connections by other nats-servers. Problem Description A client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication. Affected Versions Any version before v2.12.6 or v2.11.15 Workarounds Disable leafnode support if not needed. Restrict network …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. One authentication model supported is mTLS, deriving the NATS client identity from properties of the TLS Client Certificate. Problem Description When using mTLS for client identity, with verify_and_map to derive a NATS identity from the client certificate's Subject DN, certain patterns of RDN would not be correctly enforced, allowing …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server provides an MQTT client interface. Problem Description For MQTT deployments using usercodes/passwords: MQTT passwords are incorrectly classified as a non-authenticating identity statement (JWT) and exposed via monitoring endpoints. Affected Versions Any version before v2.12.6 or v2.11.15 Workarounds Ensure monitoring end-points are adequately secured. Best practice remains to …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server provides an optional monitoring port, which provides access to sensitive data. The nats-server can take certain configuration options on the command-line instead of requiring a configuration file. Problem Description If a nats-server is run with static credentials for all clients provided via argv (the command-line), then those …
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server provides an MQTT client interface. Problem Description When using ACLs on message subjects, these ACLs were not applied in the $MQTT.> namespace, allowing MQTT clients to bypass ACL checks for MQTT subjects. Affected Versions Any version before v2.12.6 or v2.11.15 Workarounds None.
Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server offers a WebSockets client service, used in deployments where browsers are the NATS clients. Problem Description A malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-server before authentication; this requires sending a corresponding amount of data. This is a …
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 …