CVE-2022-2601 in grub2
Summary
by MITRE • 12/15/2022
A buffer overflow was found in grub_font_construct_glyph(). A malicious crafted pf2 font can lead to an overflow when calculating the max_glyph_size value, allocating a smaller than needed buffer for the glyph, this further leads to a buffer overflow and a heap based out-of-bounds write. An attacker may use this vulnerability to circumvent the secure boot mechanism.
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Analysis
by VulDB Data Team • 05/28/2026
The vulnerability identified as CVE-2022-2601 represents a critical buffer overflow flaw within the GRUB2 bootloader's font handling mechanism. This issue specifically resides in the grub_font_construct_glyph() function which processes font data during the boot process. The vulnerability stems from improper validation of font file parameters, particularly when processing Portable Font Format 2 (PF2) font files that are commonly used in bootloader environments. The flaw occurs during the calculation of maximum glyph size values where maliciously crafted font data can manipulate the size computation to allocate insufficient buffer space for glyph rendering operations. This fundamental miscalculation creates a scenario where subsequent memory operations attempt to write beyond the allocated buffer boundaries, resulting in heap-based out-of-bounds memory corruption.
The technical exploitation of this vulnerability involves crafting a specially designed PF2 font file that triggers the flawed buffer size calculation logic. When the GRUB bootloader processes this malicious font file during boot sequence, the system allocates a buffer that is smaller than required for the actual glyph data. This discrepancy enables attackers to perform controlled out-of-bounds writes to heap memory locations, potentially allowing arbitrary code execution within the bootloader context. The vulnerability is particularly concerning because it operates at a low system level during the critical boot phase, where the system has elevated privileges and direct access to hardware components. The flaw can be categorized under CWE-121 as a stack-based buffer overflow, though the heap-based nature of the actual exploitation makes it more complex and potentially more dangerous in bootloader environments.
The operational impact of CVE-2022-2601 extends beyond simple memory corruption to threaten the fundamental security model of modern computing systems. Since GRUB2 serves as the primary bootloader for most Linux distributions and many enterprise systems, successful exploitation can bypass critical secure boot mechanisms that are designed to prevent unauthorized code execution. This vulnerability undermines the integrity of the boot process by allowing attackers to inject malicious code that can execute before the operating system loads, potentially leading to full system compromise. The attack vector is particularly insidious because it can be triggered through font files that might be encountered during normal boot operations, such as those used for display purposes in boot menus or system interfaces. The vulnerability creates a persistent threat that can survive system reboots and potentially remain undetected by traditional security monitoring systems that focus on runtime behavior rather than boot-time memory corruption.
Mitigation strategies for CVE-2022-2601 must address both immediate remediation and long-term architectural improvements. The primary solution involves updating to patched versions of GRUB2 where the font processing logic has been corrected to properly validate font parameters and prevent buffer size miscalculations. System administrators should prioritize patching affected systems, particularly those in critical infrastructure environments where secure boot mechanisms are essential. Additional protective measures include implementing strict font file validation policies that prevent unknown or untrusted font files from being processed during boot operations, and configuring bootloader settings to disable unnecessary font rendering features. Organizations should also consider implementing runtime monitoring for suspicious memory access patterns and establishing robust incident response procedures specifically designed to handle bootloader-level compromises. The vulnerability highlights the importance of securing boot-time processes and demonstrates how low-level system components can serve as critical attack vectors for bypassing higher-level security controls, aligning with ATT&CK technique T1014 for rootkit detection and prevention.