# CVE-2025-0927: serious memory overflow in Linux Kernel causes system collapse and remote code execution

## **Overview**

Recently, a serious vulnerability was discovered in the Linux Kernel, particularly affecting Ubuntu 22.04 users. The vulnerability, identified as **CVE-2025-0927**, is known for causing a heap overflow in the HFS+ file system driver of the Linux Kernel. This vulnerability allows an attacker to use a specially crafted file system image, which, when mounted, can lead to a denial of service (system crash) or even arbitrary code execution.

## **Details of the vulnerability**

* **Vulnerability ID**: CVE-2025-0927.
    
* **CVSS Score**: 8.8/10 indicating a high severity level.
    
* **Affected Range**: Linux Kernel versions from 2.6.12-rc2 to 6.12.0. Specifically, Ubuntu 22.04 with Linux Kernel 6.5.0-18-generic has been confirmed to be vulnerable.
    
* **Attack Mechanism**: The vulnerability exists in the handling of B-tree nodes of the HFS+ file system. Specifically, the lack of key length checks in the `hfs_bnode_read_key` function leads to a heap overflow.
    
* **Consequences**:
    
    * System **crash or hang**.
        
    * **Root access** and execution of malicious code.
        
    * **Data leakage or complete loss of control** over the system.
        

## **Exploitation Method**

1. **Where is the vulnerability located?**
    
    * The main vulnerability is in the **data reading line** where `key_len` is not checked for limits, especially when `key_len` comes from `hfs_bnode_read_u16()`—meaning it comes from the **content of the HFS+ file image** controlled by the attacker.
        
    * Here, the attacker will **create a fake HFS+ image** with a valid format but containing specially designed extent records to exceed the legitimate buffer size.
        
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1744074613389/2e33c506-bcc8-4c3c-89d3-04f5b1707a5b.png align="center")
    
    * In the Linux Kernel, there is a function `hfs_brec_keylen()` used to **determine key length**, which includes limit checks. However, attackers can exploit this function to copy large data, causing a heap overflow.
        
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1744075215847/f91580c8-4828-49bd-bf3c-a8e5e2cbeb42.png align="center")
    
2. **Create a fake HFS+ image**
    
    * Attackers will use the HFS+ file system creation tool (from the `hfsprogs` package)
        
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1744076789545/79e145bb-6684-48d4-812c-a10174737ffd.png align="center")
    
    ![](https://ssd-disclosure.com/wp-content/uploads/2025/03/image-20241017225408783.png align="center")
    
3. **Mount image on the target machine**
    
    * After creating a malicious HFS+ image, the attacker will use the following command to mount it on the victim's machine:
        
        `sudo mount -t hfsplus exploit.img /mnt/hfs`
        
    * Or exploit the **automount** system (by attaching it to a USB or introducing it into the CI environment)
        
4. **Trigger error**
    
    * When the Kernel reads a node leading to an unusually large `key_len`, the hacker will copy it into the heap, causing an **overflow**.
        
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1744078345206/498db37e-4ab9-4e26-83f2-fa40d1cfdf82.png align="center")
    
    * If the memory layout is predictable, the attacker can:
        
        * **Overwrite pointers**, functions, and **execute kernel code**
            
        * Cause a **denial of service (DoS)** through a crash
            

## **Detailed Impact**

* When mounting an HFS+ image with malicious data, the kernel can **crash (panic)**, causing the system to freeze.
    
* If the attacker controls the heap layout (through heap spraying or environment normalization), it can lead to **code execution in the kernel**.
    
* If a container is granted permission to mount a loop or HFS+ image, the attacker can **escape the container**.
    
* A CI system running tests with a `.img` image can experience a **complete crash** or be exploited with malicious kernel code.
    
* On Linux desktops like Ubuntu, Fedora, etc., users **only need to double-click** on a malicious HFS+ `.img` to trigger the exploit.
    

## **Recommendation**

1. **Update the Kernel as soon as possible**
    
    * sudo apt update
        
    * sudo apt upgrade
        
    * sudo reboot
        
2. **Disable HFS+ file system support if not needed**
    
    * Temporarily (until reboot)
        
        * sudo modprobe -r hfsplus
            
    * Permanently (do not load the module at boot)
        
        * Add the following line to `/etc/modprobe.d/blacklist.conf`:
            
        * **blacklist hfsplus**
            
3. **Block mounting of HFS+ file systems by unprivileged users**
    
    * **Disable auto-mounting of HFS+ devices** on desktop or server systems.
        
    * **Do not grant** `mount` permissions to users outside of root or admin groups.
        
4. **Check the system for suspicious HFS+ images**
    
5. **Monitor and log security**
    

## **Conclusion**

**CVE-2025-0927** is a critical vulnerability because it affects the kernel layer, is easy to exploit, and exists in a feature that is rarely monitored—the HFS+ file system. On Ubuntu, both Desktop and Server versions have default polkit rules that allow users with a local session to create loop devices and mount various block file systems. This bypasses the CAP\_SYS\_ADMIN restriction, allowing regular users to exploit the vulnerability.

## **Recommendation**

1. [SSD Advisory - Linux kernel hfsplus slab-out-of-bounds Write - SSD Secure Disclosure](https://ssd-disclosure.com/ssd-advisory-linux-kernel-hfsplus-slab-out-of-bounds-write/)
    
2. [CVE-2025-0927: Public Exploit Released for Linux Kernel Privilege Escalation Bug](https://securityonline.info/cve-2025-0927-public-exploit-released-for-linux-kernel-privilege-escalation-bug/)