🐧 CVE-2026-23111 - Linux Kernel nf_tables Use-After-Free Vulnerability

⚠️ Use-After-Free in Linux Kernel nf_tables

📖 Overview

CVE-2026-23111 is a high-severity Use-After-Free (UAF) vulnerability affecting the Linux kernel's netfilter/nf_tables subsystem.

The flaw originates from incorrect handling of catch-all map elements during nftables transaction rollback operations, resulting in a memory safety issue that may allow local attackers to trigger kernel memory corruption.

🎯 Vulnerability Information

🔬 Technical Analysis

The vulnerability exists in:

net/netfilter/
            └── nf_tables

During rollback of a failed transaction, the function:

nft_map_catchall_activate()

contains an inverted generation-mask validation logic.

This causes the kernel to incorrectly reactivate catch-all map elements, potentially resulting in references to memory that has already been freed.

Consequences include:

Memory corruption
Kernel crashes
Denial of Service
Potential privilege escalation

⚡ Attack Flow

┌─────────────────────┐
│ Local Attacker      │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│ nftables Operation  │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│ Transaction Failure │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│ Rollback Triggered  │
└──────────┬──────────┘
           │
           ▼
┌───────────────────────────┐
│ nft_map_catchall_activate │
│ Logic Error               │
└──────────┬────────────────┘
           │
           ▼
┌─────────────────────┐
│ Use-After-Free      │
│ Condition           │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│ Memory Corruption   │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│ Kernel Compromise   │
└─────────────────────┘

🧠 Root Cause

Expected Behavior

Rollback
   │
   ▼
Reactivate Inactive Elements

Actual Behavior

Rollback
   │
   ▼
Incorrect Generation Check
   │
   ▼
Invalid Element Activation
   │
   ▼
Use-After-Free

💥 Potential Impact

Confidentiality

🟠 Medium

Potential exposure of kernel memory.

Integrity

🔴 High

Memory corruption may allow modification of kernel structures.

Availability

🔴 High

Kernel panic and system crashes are possible.

Privilege Escalation

🔴 High

Local attackers may leverage the flaw to gain elevated privileges.

📦 Affected Component

Linux Kernel
      │
      ▼
  Netfilter
      │
      ▼
   nf_tables
      │
      ▼
Catch-all Map Elements

🔍 Detection

Monitor systems for:

Unexpected kernel crashes
nftables failures
Kernel warnings
Memory corruption alerts
Abnormal netfilter behavior
Privilege escalation attempts

Useful logs:

dmesg
journalctl -k
audit.log

🛡️ Mitigation

Recommended Actions

✓ Update Linux Kernel
✓ Apply Vendor Security Patches
✓ Restrict Local Access
✓ Monitor Kernel Logs
✓ Audit nftables Configurations
✓ Enable Security Monitoring

Verification

Check kernel version:

uname -r

Check nftables:

nft list ruleset

📊 Risk Matrix

📅 Timeline

Event	Status
Vulnerability Discovered	✅
CVE Assigned	✅
Public Disclosure	✅
Kernel Fix Released	✅

🔐 Security Recommendations

Patch Immediately
        │
        ▼
Monitor Systems
        │
        ▼
Audit nftables Usage
        │
        ▼
Restrict Untrusted Users
        │
        ▼
Maintain Kernel Updates

📚 References

Linux Kernel Security Advisories
NVD Database
Vendor Security Bulletins
Linux Kernel Commit History

🚨 Security Notice

CVE-2026-23111 demonstrates how subtle logic errors in kernel memory management can lead to serious security consequences.

Patch Early • Monitor Continuously • Secure Your Infrastructure

⭐ Star this repository if you found it useful.

CVE	CVE-2026-23111
Severity	High
CVSS v3.1	7.8
CWE	CWE-416
Vulnerability Type	Use After Free
Attack Vector	Local
Privileges Required	Low
User Interaction	None
Component	netfilter / nf_tables
Exploitation Complexity	Low

Exploitability	🟠 Medium
Privilege Escalation	🔴 High
Denial of Service	🔴 High
Memory Corruption	🔴 High
Remote Exploitation	🟢 No
Local Exploitation	🔴 Yes

CVE-2026-23111

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