CVE-2021-31250 — AI Deep Analysis Summary

Q: Root Cause? (CWE/Flaw)

🛡️ **Root Cause**: Lack of input sanitization. 🔍 **Flaw**: The system fails to clean user input when generating HTTP 404 messages. This allows raw scripts to execute in the victim's browser.

Q: Who is affected? (Versions/Components)

🏢 **Affected Vendor**: CHIYU Technology (Chiyu). 📦 **Products**: BF-630W, BF-430, BF-431, BF-450M, BF631-W, BF830-W, Webpass, bf-min-w, SEMAC. 🌐 **Context**: IoT devices for access control & attendance systems.

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

📢 **Public Exp?**: Yes. 🔗 **PoC**: Available via ProjectDiscovery Nuclei templates. 🌍 **Wild Exp**: Referenced in security blogs (Seguranca Informatica). Proof-of-concept exists for CGI endpoints.

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

🔍 **Self-Check**: Scan for CHIYU IoT devices. 🧪 **Test**: Send requests to `man.cgi`, `if.cgi`, `dhcpc.cgi`, `ppp.cgi` designed to trigger a 404 response. Check if the 404 page reflects unsanitized input.

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

🩹 **Official Fix**: Yes. 📥 **Action**: Check vendor site for firmware updates. 🔗 **Link**: CHIYU official firmware update notice (message-Firmware-update-87.htm).

Q: What if no patch? (Workaround)

🚧 **No Patch?**: Implement WAF rules. 🛡️ **Mitigation**: Block or sanitize inputs on CGI endpoints. 🔒 **Network**: Restrict access to management interfaces. Monitor for XSS payloads in 404 logs.

Q: Is it urgent? (Priority Suggestion)

🔥 **Urgency**: High. 📅 **Date**: Published June 2021. ⚖️ **Priority**: Critical for IoT security. Immediate patching or network isolation is recommended to prevent client-side hijacking.

Updated May 08, 2026

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Q1What is this vulnerability? (Essence + Consequences)

🚨 **Essence**: A Cross-Site Scripting (XSS) flaw in CHIYU IoT devices. <br>💥 **Consequences**: Attackers inject malicious client-side code.…

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Q2Root Cause? (CWE/Flaw)

🛡️ **Root Cause**: Lack of input sanitization. <br>🔍 **Flaw**: The system fails to clean user input when generating HTTP 404 messages. This allows raw scripts to execute in the victim's browser.

Q3Who is affected? (Versions/Components)

🏢 **Affected Vendor**: CHIYU Technology (Chiyu). <br>📦 **Products**: BF-630W, BF-430, BF-431, BF-450M, BF631-W, BF830-W, Webpass, bf-min-w, SEMAC. <br>🌐 **Context**: IoT devices for access control & attendance systems.

Q4What can hackers do? (Privileges/Data)

💻 **Hackers' Power**: Execute arbitrary JavaScript in the victim's browser. <br>🔓 **Impact**: Steal cookies, hijack sessions, or redirect users.…

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Q5Is exploitation threshold high? (Auth/Config)

⚠️ **Threshold**: Low to Medium. <br>🔑 **Auth**: The description mentions 'unauthenticated XSS' in the general context, but PoC targets specific CGI components (`man.cgi`, `if.cgi`, etc.).…

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

📢 **Public Exp?**: Yes. <br>🔗 **PoC**: Available via ProjectDiscovery Nuclei templates. <br>🌍 **Wild Exp**: Referenced in security blogs (Seguranca Informatica). Proof-of-concept exists for CGI endpoints.

Q7How to self-check? (Features/Scanning)

🔍 **Self-Check**: Scan for CHIYU IoT devices. <br>🧪 **Test**: Send requests to `man.cgi`, `if.cgi`, `dhcpc.cgi`, `ppp.cgi` designed to trigger a 404 response. Check if the 404 page reflects unsanitized input.

Q8Is it fixed officially? (Patch/Mitigation)

🩹 **Official Fix**: Yes. <br>📥 **Action**: Check vendor site for firmware updates. <br>🔗 **Link**: CHIYU official firmware update notice (message-Firmware-update-87.htm).

Q9What if no patch? (Workaround)

🚧 **No Patch?**: Implement WAF rules. <br>🛡️ **Mitigation**: Block or sanitize inputs on CGI endpoints. <br>🔒 **Network**: Restrict access to management interfaces. Monitor for XSS payloads in 404 logs.

Q10Is it urgent? (Priority Suggestion)

🔥 **Urgency**: High. <br>📅 **Date**: Published June 2021. <br>⚖️ **Priority**: Critical for IoT security. Immediate patching or network isolation is recommended to prevent client-side hijacking.

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