GRUB2 Squash4 Filesystem Integer Overflow Vulnerability
Overview
CVE-2025-0678 is a critical vulnerability discovered in the GRUB2 bootloader, specifically within its handling of the Squash4 filesystem. This flaw allows an attacker to exploit an integer overflow during buffer size calculations, leading to a heap-based out-of-bounds write. This vulnerability can be leveraged to corrupt GRUB's internal data structures, potentially resulting in arbitrary code execution and bypassing secure boot protections.
Vulnerability Details
CVE ID: CVE-2025-0678
Severity: 7.8 (HIGH)
Affected Software: GRUB2 versions with Squash4 filesystem support
Published Date: March 3, 2025
Technical Description
The vulnerability resides in the Squash4 filesystem module of GRUB2. When GRUB2 reads data from a Squash4 filesystem, it uses user-controlled parameters from the filesystem geometry to determine the size of an internal buffer. However, the module fails to properly check for integer overflows during these calculations.
Integer Overflow: The buffer size calculation can overflow due to improper validation of user-controlled inputs. This results in a smaller buffer being allocated than intended.
Heap-Based Out-of-Bounds Write: The
direct_read()function, which reads data into the buffer, does not account for the miscalculated buffer size. As a result, it writes data beyond the allocated buffer boundaries, corrupting adjacent memory.Exploitation: An attacker can craft a malicious Squash4 filesystem to trigger this vulnerability. By carefully controlling the filesystem geometry, they can cause GRUB2 to allocate a smaller buffer and subsequently overwrite critical data structures in memory.
Impact
Arbitrary Code Execution: An attacker can exploit this vulnerability to execute arbitrary code within the context of GRUB2.
Secure Boot Bypass: Since GRUB2 is a critical component of the boot process, this flaw can be used to bypass secure boot protections, allowing the execution of unauthorized code during system startup.
System Compromise: Successful exploitation can lead to a complete system compromise, including the installation of persistent malware or the exfiltration of sensitive data.
Sample Scenario
Consider a scenario where an attacker gains access to a system's bootloader configuration. They replace the legitimate Squash4 filesystem with a maliciously crafted one. When the system boots, GRUB2 attempts to read from this filesystem.
Crafted Filesystem: The attacker designs the filesystem geometry to trigger the integer overflow during buffer size calculation.
Buffer Allocation: GRUB2 miscalculates the buffer size due to the overflow, allocating a smaller buffer than required.
Out-of-Bounds Write: The
direct_read()function writes data beyond the allocated buffer, corrupting adjacent memory.Code Execution: The attacker's crafted data overwrites critical GRUB2 data structures, leading to the execution of arbitrary code.
Secure Boot Bypass: The attacker's code executes before the operating system loads, bypassing secure boot protections and gaining full control over the system.
Mitigation
Patch Application: Apply the latest security patches from the GRUB2 maintainers that address this vulnerability.
Secure Boot Configuration: Ensure that secure boot is properly configured and that only signed and verified bootloaders are allowed to execute.
Filesystem Validation: Implement checks to validate the integrity of the Squash4 filesystem before allowing GRUB2 to read from it.
Conclusion
CVE-2025-0678 is a severe vulnerability that underscores the importance of robust input validation and secure coding practices in critical system components like GRUB2. System administrators and users should prioritize applying patches and configuring secure boot to mitigate the risks associated with this flaw.
By understanding and addressing such vulnerabilities, we can enhance the security of our systems and protect against potential exploits that could lead to significant breaches and data loss.