# CVE-2021-29441: Authentication bypass

- Exploited (CISA KEV): no
- Published: 2021-04-27
- CVSS: 8.6 HIGH (v3.1)
- EPSS: 83.2% (100th percentile)
- CWE: CWE-290

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.

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | Before feed history | — | — |
| AWS | No public claim | — | — |
| Microsoft Azure | No public claim | — | — |
| Google Cloud | Before feed history | — | — |
| Fastly | Before feed history | — | — |
| F5 | Rule published | 2024-03-12 | 1050 |
| Akamai | No public source | — | — |
| OWASP CRS | Before feed history | — | — |

### F5

- 2024-03-12 · new · rule 200013077
  > Added: signature 200013077 "Nacos AuthFilter Authentication Bypass" (Authentication/Authorization Attacks, risk High), systems: Java Servlets/JSP. References: CVE-2021-29441.
  Source: https://docs.cloud.f5.com/docs-v2/platform/changelogs/security-details-changelog

## Our test (measured)

- OWASP Core Rule Set 4.25.0, paranoia level 1, anomaly threshold 5, default CRS settings: passed (0 of 2 requests blocked), template CVE-2021-29441, 2026-11-02
- OWASP Core Rule Set 4.25.0, paranoia level 2, anomaly threshold 5, default CRS settings: passed (0 of 2 requests blocked), template CVE-2021-29441, 2026-11-02

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

HTML: https://cve.vigilbase.com/cve/CVE-2021-29441 · JSON: https://cve.vigilbase.com/api/v1/cves/CVE-2021-29441