CVE-2025-21764 — AI Deep Analysis Summary

🚨 **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.

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

📦 **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.

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

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

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

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

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

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

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