Overview
A security vulnerability, identified as CVE-2025-61664, has been discovered in the GRUB2 bootloader. This flaw is categorized as a Use-After-Free (UAF) issue within the `normal` module. Specifically, the `normal_exit` command isn’t properly unregistered when its associated module is unloaded. This can be exploited by an attacker to trigger a system crash or potentially compromise data confidentiality and integrity.
Technical Details
The root cause of this vulnerability lies in the improper management of memory allocated for the `normal_exit` command within the GRUB2 `normal` module. When the module containing this command is unloaded, the command’s associated data structures are not correctly cleared or unregistered. Consequently, if an attacker manages to invoke the `normal_exit` command after the module has been unloaded, the system attempts to access memory that has already been freed. This Use-After-Free condition leads to unpredictable behavior, including system crashes.
The vulnerability is triggered by a specific sequence of events:
- A GRUB2 configuration file (or another mechanism) allows the `normal` module to be loaded.
- The system operates such that the `normal` module is subsequently unloaded (e.g., through a specific GRUB2 command or configuration change).
- An attacker can then manipulate the system to invoke the `normal_exit` command. Since the module containing this command has been unloaded, it results in the UAF condition.
CVSS Analysis
The Common Vulnerability Scoring System (CVSS) assigns CVE-2025-61664 a score of 4.9 (Medium).
- CVSS Score: 4.9
- Vector String: (The specific vector string would be available on the NVD website, once published)
- Explanation: While a system crash can be disruptive, the exploitability and impact on confidentiality/integrity are considered moderate. Successful exploitation requires a specific chain of events and potentially some level of privileged access to manipulate the GRUB2 environment.
Possible Impact
Exploitation of CVE-2025-61664 can have several negative consequences:
- System Crash: The most likely outcome is a system crash, leading to downtime and potential data loss if the system was in the middle of writing to disk.
- Data Confidentiality Compromise (Potentially): While less likely, a successful exploit could potentially lead to information disclosure if the freed memory contains sensitive data.
- Data Integrity Compromise (Potentially): In rare cases, exploitation could corrupt data if the freed memory is reallocated and overwritten with malicious content before the access.
The actual impact will depend on the specific system configuration and the attacker’s capabilities.
Mitigation and Patch Steps
The primary mitigation for CVE-2025-61664 is to apply the official patch provided by your operating system vendor or GRUB2 maintainers. Follow these steps:
- Check for Updates: Regularly check for updates to your GRUB2 installation. Use your operating system’s package manager (e.g., `apt update && apt upgrade` on Debian/Ubuntu, `yum update` on CentOS/RHEL).
- Apply Patches: Install any available patches that address CVE-2025-61664.
- Monitor Security Advisories: Stay informed about security advisories from your operating system vendor and the GRUB2 project.
- Restrict GRUB2 Access: Limit access to the GRUB2 configuration to authorized personnel only. Implement strong authentication mechanisms to prevent unauthorized modifications.
Contact your OS vendor for the specific patch. Check the references for more details.
