CVE-2021-29441: Authentication bypass

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 83.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-04-27 · updated 2026-06-17
Weakness: CWE-290

Description

Nacos is a platform designed for dynamic service discovery and configuration and service management. In Nacos before version 1.4.1, when configured to use authentication (-Dnacos.core.auth.enabled=true) Nacos uses the AuthFilter servlet filter to enforce authentication. This filter has a backdoor that enables Nacos servers to bypass this filter and therefore skip authentication checks. This mechanism relies on the user-agent HTTP header so it can be easily spoofed. This issue may allow any user to carry out any administrative tasks on the Nacos server.

Affected products

alibaba nacos: before 1.4.1 — fixed in 1.4.1

How to fix

Upgrade to a fixed version: alibaba nacos 1.4.1. Check the vendor advisory for mitigations.

References

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