CVE-2025-21764 — AI Deep Analysis Summary

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

🚨 **Essence**: The `ndisc_alloc_skb` function is not protected by RCU. 💥 **Consequence**: May trigger **Use-After-Free (UAF)**. ⚠️ Can lead to system crashes or privilege escalation risks.

Q: Root Cause? (CWE/Flaw)

🔍 **Root Cause**: **Resource management error** (CWE-416). ❌ `ndisc_alloc_skb` lacks **RCU synchronization mechanism**. 🧨 Leads to dangling pointer being accessed again.

Q: Who is affected? (Versions/Components)

📦 **Affected Component**: Linux kernel's `ndisc_alloc_skb`. 🖥️ **Affected Versions**: Kernel versions containing the defect (see fix commits for details). 🎯 All network layer scenarios using this function.

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

🕵️ **Attacker Capability**: - No need to directly read data. - Can **corrupt kernel structures** → potential **privilege escalation** / **DoS**. 💣 System stability is threatened.

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

✅ **Exploitation Difficulty**: Low to medium. 🔑 **No authentication required**. ⚙️ Depends on specific network configuration to trigger `ndisc_alloc_skb`.

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

🧪 **Ready-made Exploit**: None. 📂 **PoC**: Not publicly available yet. 🌐 **In-the-wild Exploitation**: Data not mentioned.

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

🔎 **Self-check Method**: - Check if kernel version contains the defective code. - Compare with fix commit hashes: - `96fc896d0e5...` - `3c2d705f5ad...` etc. 🛠️ Use Git history to verify.

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

🛡️ **Official Fix**: Fixed. 📜 Patches submitted to multiple stable branches. 🔗 Example: `https://git.kernel.org/stable/c/96fc896d0e5...` ✅ Introduced RCU protection mechanism.

Q: What if no patch? (Workaround)

⚠️ **When No Patch Available**: - Restrict IPv6 NDISC related traffic. - Disable unnecessary network features to reduce attack surface. 🚧 Temporary mitigation ≠ permanent fix.

Q: Is it urgent? (Priority Suggestion)

🔥 **Priority**: High! 📌 Involves kernel UAF, high risk. 🕒 Upgrade to fixed version or apply patch as soon as possible.

Updated Apr 23, 2026 CVSS 7.8 · 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**: The `ndisc_alloc_skb` function is not protected by RCU.
💥 **Consequence**: May trigger **Use-After-Free (UAF)**.
⚠️ Can lead to system crashes or privilege escalation risks.

Q2Root Cause? (CWE/Flaw)

🔍 **Root Cause**: **Resource management error** (CWE-416).
❌ `ndisc_alloc_skb` lacks **RCU synchronization mechanism**.
🧨 Leads to dangling pointer being accessed again.

Q3Who is affected? (Versions/Components)

📦 **Affected Component**: Linux kernel's `ndisc_alloc_skb`.
🖥️ **Affected Versions**: Kernel versions containing the defect (see fix commits for details).
🎯 All network layer scenarios using this function.

Q4What can hackers do? (Privileges/Data)

🕵️ **Attacker Capability**:
- No need to directly read data.
- Can **corrupt kernel structures** → potential **privilege escalation** / **DoS**.
💣 System stability is threatened.

Q5Is exploitation threshold high? (Auth/Config)

✅ **Exploitation Difficulty**: Low to medium.
🔑 **No authentication required**.
⚙️ Depends on specific network configuration to trigger `ndisc_alloc_skb`.

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

🧪 **Ready-made Exploit**: None.
📂 **PoC**: Not publicly available yet.
🌐 **In-the-wild Exploitation**: Data not mentioned.

Q7How to self-check? (Features/Scanning)

🔎 **Self-check Method**:
- Check if kernel version contains the defective code.
- Compare with fix commit hashes:
  - `96fc896d0e5...`
  - `3c2d705f5ad...` etc.
🛠️ Use Git history to verify.

Q8Is it fixed officially? (Patch/Mitigation)

🛡️ **Official Fix**: Fixed.
📜 Patches submitted to multiple stable branches.
🔗 Example: `https://git.kernel.org/stable/c/96fc896d0e5...`
✅ Introduced RCU protection mechanism.

Q9What if no patch? (Workaround)

⚠️ **When No Patch Available**:
- Restrict IPv6 NDISC related traffic.
- Disable unnecessary network features to reduce attack surface.
🚧 Temporary mitigation ≠ permanent fix.

Q10Is it urgent? (Priority Suggestion)

🔥 **Priority**: High!
📌 Involves kernel UAF, high risk.
🕒 Upgrade to fixed version or apply patch as soon as possible.

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