CVE-2026-29785

NATS Server panic via malicious compression on leafnode port

CVSS 3.1 7.5 HIGHEUVD CVSS 3.1 7.5 CVSS 3.1 · [email protected] · Secondary 7.5 HIGHCVSS 3.1 · 0b0ca135-0b70-47e7-9f44-1890c2a1c46c · Secondary 7.5 HIGHCVSS_V3 Publisher rating HIGHFixed by github.com/nats-io/nats-server/v2 2.11.14 Fixed by github.com/nats-io/nats-server/v2 2.12.5osv · severity unknownFixed by github.com/nats-io/nats-server/v2 2.11.14 Fixed by github.com/nats-io/nats-server/v2 2.12.5KEV status unknown

Original advisory

cve-program · CVE-2026-29785

Published

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.14 and 2.12.5, if the nats-server has the "leafnode" configuration enabled (not default), then anyone who can connect can crash the nats-server by triggering a panic. This happens pre-authentication and requires that compression be enabled (which it is, by default, when leafnodes are used). Versions 2.11.14 and 2.12.5 contain a fix. As a workaround, disable compression on the leafnode port.

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euvd · EUVD-2026-15963

Published

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nvd · CVE-2026-29785

Published

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osv · GHSA-52jh-2xxh-pwh6

Published

### 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 can connect can crash the nats-server by triggering a panic. This happens pre-authentication and requires that compression be enabled (which it is, by default, when leafnodes are used). Context: a NATS server can form various clustering topologies, including local clusters, and superclusters of clusters, but leafnodes allow for separate administrative domains to link together with limited data communication; eg, a server in a moving vehicle might use a local leafnode for agents to connect to, and sync up to a central service as and when available. The leafnode configuration here is where the central server allows other NATS servers to connect into it, almost like regular NATS clients. Documentation examples typically use port 7422 for leafnode communications. ### Affected Versions Version 2, prior to v2.11.14 or v2.12.5 ### Workarounds Disable compression on the leafnode port: ``` leafnodes { port: 7422 compression: off } ```

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osv · GO-2026-4829

Published

NATS Server panic via malicious compression on leafnode port in github.com/nats-io/nats-server

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Affected versions, risk and source history

Exploitation and risk

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Advisory history

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15 Nov 2026 09:29:42 UTC