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CVE-2026-58253 nats-io CVE debrief

CVE-2026-58253 is an authentication bypass vulnerability in NATS Server. Prior to versions 2.14.0, 2.12.7, and 2.11.16, when no_auth_user was configured, a parser fast path intended for ordinary client connections could also apply to route or leafnode listeners. This allowed an unauthenticated peer to bypass inter-server CONNECT authentication and operate with the privileges associated with that connection type. The vulnerability affects NATS Server and has a high CVSS score of 8.8.

Vendor
nats-io
Product
nats-server
CVSS
HIGH 8.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-08
Original CVE updated
2026-07-13
Advisory published
2026-07-08
Advisory updated
2026-07-13

Who should care

Users of NATS Server, especially those using versions prior to 2.14.0, 2.12.7, and 2.11.16, should be aware of this vulnerability and take steps to mitigate it. This includes upgrading to a patched version and reviewing their configuration for potential vulnerabilities. Operators, platform administrators, and security teams should review the vulnerability and take necessary actions to protect their systems.

Technical summary

The vulnerability exists in the NATS Server's handling of connections when no_auth_user is configured. A parser fast path intended for ordinary client connections could also be applied to route or leafnode listeners, allowing an unauthenticated peer to bypass inter-server CONNECT authentication. This could enable an attacker to operate with elevated privileges. The affected product is NATS Server, and the vulnerability is related to authentication bypass.

Defensive priority

High

Recommended defensive actions

  • Upgrade to NATS Server version 2.14.0, 2.12.7, or 2.11.16, or later
  • Review and adjust the no_auth_user configuration
  • Monitor for suspicious activity and implement compensating controls
  • Verify and validate user privileges and access controls
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record was published on 2026-07-08T20:16:54.943Z and last modified on 2026-07-13T15:25:44.430Z. The NVD entry is currently Analyzed. This information is based on the NVD entry and the CVE record. The vulnerability affects NATS Server versions prior to 2.14.0, 2.12.7, and 2.11.16. The evidence is limited to the information provided in the CVE record and NVD entry.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-58253 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-58253

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-58253 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-58253

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.