CVE-2021-29441 — AI Deep Analysis Summary

Q: What is this vulnerability? (Essence + Consequences)

🚨 **Essence**: Nacos Auth Bypass via User-Agent spoofing. 💥 **Consequences**: Attackers skip authentication checks entirely. 📉 **Impact**: Full administrative control over the service discovery & config platform.

Q: Root Cause? (CWE/Flaw)

🛡️ **CWE-290**: Authentication Bypass by Spoofing. 🔍 **Flaw**: The `AuthFilter` relies on the `User-Agent` HTTP header. ⚠️ **Mechanism**: Servers can spoof this header to bypass the filter logic.

Q: Who is affected? (Versions/Components)

🏢 **Vendor**: Alibaba. 📦 **Product**: Nacos. 📅 **Affected**: Versions **before 1.4.1**. 🔑 **Condition**: Must have `nacos.core.auth.enabled=true`.

Q: What can hackers do? (Privileges/Data)

👑 **Privileges**: Full Admin Rights. 👤 **Actions**: Create accounts, modify configs, manage services. 📊 **Data**: Access to all dynamic service discovery data.

Q: Is exploitation threshold high? (Auth/Config)

📉 **Threshold**: LOW. 🔓 **Auth**: None required (if spoofed). 🌐 **Network**: Remote (AV:N). 🎯 **Complexity**: Low (AC:L).

Q: Is there a public Exp? (PoC/Wild Exploitation)

🔥 **Exploits**: YES. 📂 **PoCs**: Multiple GitHub repos (e.g., `hh-hunter`, `bysinks`). 🛠️ **Tools**: Nuclei templates available. 🚀 **Status**: Wild exploitation possible.

Q: How to self-check? (Features/Scanning)

🔍 **Check**: Scan for Nacos instances. 🧪 **Test**: Send requests with spoofed User-Agent. 📡 **Scan**: Use Nuclei template `CVE-2021-29441.yaml`. 👀 **Verify**: Check if admin endpoints respond without login.

Q: Is it fixed officially? (Patch/Mitigation)

✅ **Fixed**: YES. 🔧 **Patch**: Upgrade to **Nacos 1.4.1** or later. 📝 **Ref**: GitHub PR #4703. 🔒 **Action**: Mandatory update for security.

Q: Is it urgent? (Priority Suggestion)

🔴 **Priority**: CRITICAL. 🚨 **Urgency**: HIGH. 📢 **Reason**: Remote, unauthenticated, full admin bypass. ⏱️ **Action**: Patch immediately. Do not delay.

Updated May 06, 2026 CVSS 8.6 · High

This is a summary of the AI-generated 10-question deep analysis. The full version (longer answers, follow-up Q&A, related CVEs) requires login. Read the full analysis →

Q1What is this vulnerability? (Essence + Consequences)

🚨 **Essence**: Nacos Auth Bypass via User-Agent spoofing. <br>💥 **Consequences**: Attackers skip authentication checks entirely. <br>📉 **Impact**: Full administrative control over the service discovery & config platform.

Q2Root Cause? (CWE/Flaw)

🛡️ **CWE-290**: Authentication Bypass by Spoofing. <br>🔍 **Flaw**: The `AuthFilter` relies on the `User-Agent` HTTP header. <br>⚠️ **Mechanism**: Servers can spoof this header to bypass the filter logic.

Q3Who is affected? (Versions/Components)

🏢 **Vendor**: Alibaba. <br>📦 **Product**: Nacos. <br>📅 **Affected**: Versions **before 1.4.1**. <br>🔑 **Condition**: Must have `nacos.core.auth.enabled=true`.

Q4What can hackers do? (Privileges/Data)

👑 **Privileges**: Full Admin Rights. <br>👤 **Actions**: Create accounts, modify configs, manage services. <br>📊 **Data**: Access to all dynamic service discovery data.

Q5Is exploitation threshold high? (Auth/Config)

📉 **Threshold**: LOW. <br>🔓 **Auth**: None required (if spoofed). <br>🌐 **Network**: Remote (AV:N). <br>🎯 **Complexity**: Low (AC:L).

Q6Is there a public Exp? (PoC/Wild Exploitation)

🔥 **Exploits**: YES. <br>📂 **PoCs**: Multiple GitHub repos (e.g., `hh-hunter`, `bysinks`). <br>🛠️ **Tools**: Nuclei templates available. <br>🚀 **Status**: Wild exploitation possible.

Q7How to self-check? (Features/Scanning)

🔍 **Check**: Scan for Nacos instances. <br>🧪 **Test**: Send requests with spoofed User-Agent. <br>📡 **Scan**: Use Nuclei template `CVE-2021-29441.yaml`. <br>👀 **Verify**: Check if admin endpoints respond without login.

Q8Is it fixed officially? (Patch/Mitigation)

✅ **Fixed**: YES. <br>🔧 **Patch**: Upgrade to **Nacos 1.4.1** or later. <br>📝 **Ref**: GitHub PR #4703. <br>🔒 **Action**: Mandatory update for security.

Q9What if no patch? (Workaround)

🚧 **Workaround**: If upgrade impossible, restrict network access. <br>🚫 **Block**: Prevent external access to Nacos ports. <br>🛡️ **WAF**: Block spoofed User-Agent patterns (if feasible).…

Read full answer (login)

Q10Is it urgent? (Priority Suggestion)

🔴 **Priority**: CRITICAL. <br>🚨 **Urgency**: HIGH. <br>📢 **Reason**: Remote, unauthenticated, full admin bypass. <br>⏱️ **Action**: Patch immediately. Do not delay.

Continue exploring

Vulnerability detail Full AI analysis (login) alibaba CWE-290