Linux Kernel, Out-of-Bounds (OoB) Access, CVE-2025-21789 (Critical)

How the Mentioned CVE Works:

CVE-2025-21789 is a critical vulnerability in the Linux kernel, specifically affecting the LoongArch architecture’s IP checksum implementation. The issue arises due to an undefined shift and out-of-bounds (OoB) read when processing negative lengths in the checksum calculation. This vulnerability was introduced by commit 69e3a6aa6be2, which aimed to optimize checksum calculations for 64-bit systems. The flaw allows an attacker to trigger an OoB access, potentially leading to system crashes, information disclosure, or remote code execution. A similar issue was previously fixed in the ARM64 architecture via commit 8bd795fedb84. The CVSS 4.0 severity score highlights the critical nature of this vulnerability, emphasizing the need for immediate patching.

DailyCVE Form:

Platform: Linux Kernel
Version: LoongArch-based systems
Vulnerability: Out-of-Bounds (OoB) Access
Severity: Critical
Date: 02/26/2025

(End of form)

What Undercode Say:

Analytics:

• Affected Systems: Linux kernels with LoongArch architecture and checksum optimization enabled.
• Attack Vector: Local or remote exploitation depending on system configuration.
• Impact: System crashes, data leaks, or potential remote code execution.

Exploitation:

1. Trigger OoB Access: Craft a malicious packet with a negative length to exploit the checksum calculation.
2. Payload Delivery: Use the OoB read to leak memory or crash the system.
3. Privilege Escalation: Combine with other vulnerabilities for full system compromise.

Protection:

1. Patch: Apply the latest kernel update from the official Linux kernel repository.
2. Mitigation: Disable checksum optimization if patching is not immediately possible.
3. Monitoring: Use intrusion detection systems (IDS) to detect abnormal network activity.

Commands:

• Check kernel version:

  uname -r
  

• Update kernel:

  sudo apt-get update && sudo apt-get install linux-image-$(uname -r)
  

• Verify patch:

  grep -r "69e3a6aa6be2" /usr/src/linux
  

Code:

• Exploit PoC (for educational purposes only):

  // Craft malicious packet with negative length
  struct packet {
  int length;
  char data[1024];
  };
  packet p;
  p.length = -1;
  send_packet(&p);
  

• Patch Verification:

  // Check for OoB fix in kernel source
  if (length < 0) {
  return -EINVAL;
  }
  

URLs:

• Linux Kernel Git Repository
• CVE Details
• LoongArch Documentation

Additional Tools:

• GDB: Debug kernel crashes caused by OoB access.
• KASAN: Detect memory corruption vulnerabilities in the kernel.
• Snort: Monitor network traffic for malicious packets.
  By following these steps, users can mitigate the risks associated with CVE-2025-21789 and ensure system security.

References:

Reported By: https://nvd.nist.gov/vuln/detail/CVE-2025-21789
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