CVE-2026-58253
Description
A flaw was found in NATS Server. When the no_auth_user configuration is enabled, a parser optimization intended for client connections can inadvertently apply to route or leafnode listeners. This allows an unauthenticated attacker on an adjacent network to bypass inter-server authentication. Consequently, the attacker can operate with the privileges of a trusted connection, leading to a high impact on data integrity.
Statement
This Important flaw in NATS Server permits an unauthenticated attacker on an adjacent network to bypass inter-server authentication when the no_auth_user configuration is active. This allows the attacker to operate with trusted connection privileges, leading to a high impact on data integrity.
Mitigation
To mitigate this issue, avoid enabling the `no_auth_user` configuration in NATS Server. If `no_auth_user` is required, restrict network access to NATS route and leafnode listeners using firewall rules to only trusted hosts and networks. This limits the attack surface by preventing unauthenticated access from adjacent networks. A restart of the NATS server may be required for configuration changes to take effect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.8 | N/A | 8.8 |
| Attack Vector | Adjacent Network | N/A | Adjacent Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Changed | N/A | Changed |
| Confidentiality | Low | N/A | Low |
| Integrity Impact | High | N/A | High |
| Availability Impact | Low | N/A | Low |
Vector
Red Hat: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L
cve.org: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
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