Answer in brief
CVE-2026-27889 records a High severity (CVSS 7.5) vulnerability in NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead. The current sources do not mark it as known exploited. The current feed maps nats-io/nats-server (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
Answer in brief
CVE-2026-27889 records a High severity (CVSS 7.5) vulnerability in NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead. The current sources do not mark it as known exploited. The current feed maps nats-io/nats-server (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps nats-io/nats-server (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| nats-io/nats-servergeneric | >= 2.2.0, < 2.11.14 || >= 2.12.0, < 2.12.5 | Not reported |
Published upstream
Mar 25, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 3, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 15, 2026
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.
Quoted source text, attributed separately from HOL analysis.
CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps nats-io/nats-server (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| nats-io/nats-servergeneric | >= 2.2.0, < 2.11.14 || >= 2.12.0, < 2.12.5 | Not reported |
Published upstream
Mar 25, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 3, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 15, 2026
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.
Quoted source text, attributed separately from HOL analysis.