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Authentication bypass

Not in CISA KEVCVE-2021-29441CWE-290

Not confirmed exploited. 1 of 8 rule sources name it. Our CRS test: not blocked.

Edge rules
1/8
Our test
Not blocked
CVSS
8.6
EPSS
83.2% Top 0.3%
Posts, 14d
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Published
2021-04-27
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… More

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.

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Ask about CVE-2021-29441: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

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Severity, decoded

CVSS 3.1
High · 8.6 / 10

Exploitable over the network, with no privileges and no user interaction, leading to full loss of confidentiality, and the impact can reach components beyond the vulnerable one.

Over the internetNo login neededNo user actionWorks reliablySpreads beyond the appSerious impact
How the score is built8 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo special conditions are needed; the attack works reliably.
    Low
  • Privileges requiredNo account or login is needed.
    None
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • ScopeThe attack can spread beyond the vulnerable component to other parts of the system.
    Changed
  • Confidentiality impactAn attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impactData cannot be changed by the attacker.
    None
  • Availability impactThe component keeps working normally.
    None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Public exploits

1 found
0 Metasploit0 Exploit-DB1 Scanner template0 GitHub PoCs

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2021-04-27
    CVE published
    CVE List
  2. 2024-03-12
    F5 ships a rule
    Nacos AuthFilter Authentication Bypass
  3. 2026-11-02
    Our test: OWASP Core Rule Set let it through
    paranoia level 1, anomaly threshold 5, default CRS settings
  4. 2026-11-02
    Our test: OWASP Core Rule Set let it through
    paranoia level 2, anomaly threshold 5, default CRS settings

Social

2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed RulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)1 quoteRule published

First rule 2024-03-12, 1050 days after the CVE was published.

2024-03-12New rule200013077Source
Added: signature 200013077 "Nacos AuthFilter Authentication Bypass" (Authentication/Authorization Attacks, risk High), systems: Java Servlets/JSP. References: CVE-2021-29441.
AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)Before feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.