CVE-2026-21881 — AI Deep Analysis Summary

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

🚨 **Essence**: Kanboard < 1.2.48 has a critical **Auth Bypass** flaw. ⚡ **Consequences**: Attackers can impersonate **ANY user**. Total loss of identity integrity. Data exposure is high.

Q: Root Cause? (CWE/Flaw)

🛡️ **Root Cause**: **CWE-287** (Improper Authentication). ❌ **Flaw**: Logic error when `REVERSE_PROXY_AUTH` is enabled. The system fails to validate the proxy header correctly.

Q: Who is affected? (Versions/Components)

📦 **Affected**: **Kanboard** (Open Source Task Board). 📉 **Versions**: **1.2.48 and earlier**. 🔧 **Component**: Authentication module interacting with reverse proxies.

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

💀 **Attacker Actions**: 1️⃣ **Impersonate** any user (Admin/User). 2️⃣ **Read** private tasks/boards. 3️⃣ **Modify** project data. 📊 **Impact**: High Confidentiality & Integrity loss.

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

⚠️ **Threshold**: **LOW**. 🔑 **Auth**: None required (PR:N). 🌐 **Network**: Remote (AV:N). ⚙️ **Config**: Only if `REVERSE_PROXY_AUTH` is ON. Easy to trigger if configured.

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

🚫 **Public Exp?**: **No**. 📝 **PoC**: Empty in data. 🌍 **Wild Exp**: Unlikely yet. But the flaw is logical and simple, so PoCs may appear soon.

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

🔍 **Self-Check**: 1️⃣ Check Kanboard version (Is it < 1.2.49?). 2️⃣ Check `config.php` for `REVERSE_PROXY_AUTH`. 3️⃣ Scan for Kanboard instances exposed to reverse proxies.

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

✅ **Fixed?**: **YES**. 🔧 **Patch**: Upgrade to **v1.2.49**. 🔗 **Ref**: GitHub Advisory GHSA-wwpf-3j4p-739w. Commit 7af6143 fixes it.

Q: What if no patch? (Workaround)

🛡️ **No Patch?**: 1️⃣ **Disable** `REVERSE_PROXY_AUTH` immediately. 2️⃣ Use standard Kanboard login. 3️⃣ Restrict access via WAF/Network ACLs.

Q: Is it urgent? (Priority Suggestion)

🔥 **Urgency**: **CRITICAL**. 🚨 **Priority**: **P0**. 💡 **Reason**: Remote Auth Bypass = Full Account Takeover. Patch immediately to prevent data breach.

Updated May 06, 2026 CVSS 9.1 · Critical

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**: Kanboard < 1.2.48 has a critical **Auth Bypass** flaw. <br>⚡ **Consequences**: Attackers can impersonate **ANY user**. Total loss of identity integrity. Data exposure is high.

Q2Root Cause? (CWE/Flaw)

🛡️ **Root Cause**: **CWE-287** (Improper Authentication). <br>❌ **Flaw**: Logic error when `REVERSE_PROXY_AUTH` is enabled. The system fails to validate the proxy header correctly.

Q3Who is affected? (Versions/Components)

📦 **Affected**: **Kanboard** (Open Source Task Board). <br>📉 **Versions**: **1.2.48 and earlier**. <br>🔧 **Component**: Authentication module interacting with reverse proxies.

Q4What can hackers do? (Privileges/Data)

💀 **Attacker Actions**: <br>1️⃣ **Impersonate** any user (Admin/User). <br>2️⃣ **Read** private tasks/boards. <br>3️⃣ **Modify** project data. <br>📊 **Impact**: High Confidentiality & Integrity loss.

Q5Is exploitation threshold high? (Auth/Config)

⚠️ **Threshold**: **LOW**. <br>🔑 **Auth**: None required (PR:N). <br>🌐 **Network**: Remote (AV:N). <br>⚙️ **Config**: Only if `REVERSE_PROXY_AUTH` is ON. Easy to trigger if configured.

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

🚫 **Public Exp?**: **No**. <br>📝 **PoC**: Empty in data. <br>🌍 **Wild Exp**: Unlikely yet. But the flaw is logical and simple, so PoCs may appear soon.

Q7How to self-check? (Features/Scanning)

🔍 **Self-Check**: <br>1️⃣ Check Kanboard version (Is it < 1.2.49?). <br>2️⃣ Check `config.php` for `REVERSE_PROXY_AUTH`. <br>3️⃣ Scan for Kanboard instances exposed to reverse proxies.

Q8Is it fixed officially? (Patch/Mitigation)

✅ **Fixed?**: **YES**. <br>🔧 **Patch**: Upgrade to **v1.2.49**. <br>🔗 **Ref**: GitHub Advisory GHSA-wwpf-3j4p-739w. Commit 7af6143 fixes it.

Q9What if no patch? (Workaround)

🛡️ **No Patch?**: <br>1️⃣ **Disable** `REVERSE_PROXY_AUTH` immediately. <br>2️⃣ Use standard Kanboard login. <br>3️⃣ Restrict access via WAF/Network ACLs.

Q10Is it urgent? (Priority Suggestion)

🔥 **Urgency**: **CRITICAL**. <br>🚨 **Priority**: **P0**. <br>💡 **Reason**: Remote Auth Bypass = Full Account Takeover. Patch immediately to prevent data breach.

Continue exploring

Vulnerability detail Full AI analysis (login) kanboard CWE-287