CVE-2026-27889: linuxfoundation nats-server Integer Overflow or Wraparound

Vulnerability summary

CVE-2026-27889 is a high (CVSS 7.5) Integer Overflow or Wraparound vulnerability in linuxfoundation nats-server. EPSS estimates a 0.84% chance of exploitation in the next 30 days, higher than 57.2% of scored vulnerabilities.

Timeline

1. 25-03-2026
   PublishedVulnerability first disclosed.
2. 09-09-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-190Integer Overflow or WraparoundThe product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
• CWE-1286Improper Validation of Syntactic Correctness of InputThe product receives input that is expected to be well-formed - i.e., to comply with a certain syntax - but it does not validate or incorrectly validates that the input complies with the syntax.