NATS: Leafnode connections allow spoofing of Nats-Request-Info identity headers

Medium6.4CVE-2026-33246 · Published Mar 24, 2026 · updated Sep 10, 2026

### 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 own decisions on how to trust a message, provided that they trust the nats-server as a broker. A leafnode connecting to a nats-server is not fully trusted unless the system account is bridged too. Thus identity claims should not have propagated unchecked. Thus NATS clients relying upon the Nats-Request-Info: header could be spoofed. Does not directly affect the nats-server itself, but the CVSS Confidentiality and Integrity scores are based upon what a hypothetical client might choose to do with this NATS header. ### Affected Versions Any version before v2.12.6 or v2.11.15 ### Workarounds None.