Question 1

What is this vulnerability? (Essence + Consequences)

Accepted Answer

🚨 **Essence**: HAProxy has an input validation error in `htx_add_header()` and `htx_add_trailer()`.…

Question 2

Root Cause? (CWE/Flaw)

Accepted Answer

🔍 **Root Cause**: **Integer Overflow** leading to insufficient input validation.
🛑 **Flaw**: The functions fail to check the length of header names properly.…

Question 3

Who is affected? (Versions/Components)

Accepted Answer

🏢 **Vendor**: HAProxy (HAProxy Technologies).
📦 **Product**: HAProxy (Open-source TCP/HTTP Load Balancer).
📅 **Affected**: Versions prior to the fix released around **September 2021**.…

Question 4

What can hackers do? (Privileges/Data)

Accepted Answer

💀 **Attacker Actions**:
1. **Bypass Security Rules**: Access restricted paths (e.g., `/admin`) that HAProxy explicitly denies.
2.…

Question 5

Is exploitation threshold high? (Auth/Config)

Accepted Answer

⚡ **Threshold**: **Low**.
🔓 **Auth**: No authentication required.
⚙️ **Config**: Exploits the core parsing logic of HAProxy.
🎯 **Ease**: Simple HTTP requests can trigger the integer overflow.…

Question 6

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

Accepted Answer

🔥 **Public Exploits**: **YES**.
📂 **PoCs**: Multiple GitHub repositories exist (e.g., `knqyf263/CVE-2021-40346`, `donky16/CVE-2021-40346-POC`).…

Question 7

How to self-check? (Features/Scanning)

Accepted Answer

🔎 **Self-Check**:
1. **Scan**: Use tools detecting HAProxy version < 2.2.17 (or patched version).
2. **Test**: Send crafted headers with specific length patterns to trigger integer overflow.
3.…

Question 8

Is it fixed officially? (Patch/Mitigation)

Accepted Answer

🛡️ **Official Fix**: **YES**.
📝 **Patch**: HAProxy released a fix (Commit `3b69886f...`).
📢 **Advisory**: Fedora and other distros issued updates (e.g., `FEDORA-2021-cd5ee418f6`).…

Question 9

What if no patch? (Workaround)

Accepted Answer

🚧 **No Patch Workaround**:
1. **WAF**: Deploy a Web Application Firewall to filter malformed headers.
2.…

Question 10

Is it urgent? (Priority Suggestion)

Accepted Answer

🔴 **Urgency**: **HIGH**.
⚠️ **Priority**: Critical.
📉 **Impact**: Allows bypassing access controls and potential data injection.
🚀 **Recommendation**: Patch immediately.…

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CVE-2021-40346 — AI Deep Analysis Summary

Q1What is this vulnerability? (Essence + Consequences)

Q2Root Cause? (CWE/Flaw)

Q3Who is affected? (Versions/Components)

Q4What can hackers do? (Privileges/Data)

Q5Is exploitation threshold high? (Auth/Config)

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

Q7How to self-check? (Features/Scanning)

Q8Is it fixed officially? (Patch/Mitigation)

Q9What if no patch? (Workaround)

Q10Is it urgent? (Priority Suggestion)

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