CVE-2022-3775 in grub2
Summary
by MITRE • 12/19/2022
When rendering certain unicode sequences, grub2's font code doesn't proper validate if the informed glyph's width and height is constrained within bitmap size. As consequence an attacker can craft an input which will lead to a out-of-bounds write into grub2's heap, leading to memory corruption and availability issues. Although complex, arbitrary code execution could not be discarded.
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Analysis
by VulDB Data Team • 05/28/2026
The vulnerability identified as CVE-2022-3775 resides within the grub2 bootloader's font rendering subsystem, specifically exposing a critical memory corruption flaw that stems from inadequate input validation during glyph processing. This issue manifests when grub2 encounters certain unicode character sequences that require font rendering, creating a scenario where the software fails to properly constrain glyph dimensions against the allocated bitmap boundaries. The root cause aligns with CWE-129, representing an insufficient bounds check on the width and height parameters of font glyphs, which allows attackers to manipulate these values beyond the intended memory constraints.
The technical exploitation of this vulnerability occurs through crafted unicode input sequences that deliberately exceed the predefined bitmap dimensions when processed by grub2's font rendering engine. When the bootloader attempts to render these maliciously constructed glyphs, the insufficient validation permits out-of-bounds memory writes to occur within the heap memory space allocated for font data structures. This memory corruption can manifest in various ways including heap corruption, pointer overwrites, or other forms of memory instability that fundamentally compromise the bootloader's operational integrity and memory management mechanisms. The vulnerability's classification as a heap-based buffer overflow directly corresponds to CWE-122, which specifically addresses improper restriction of operations within the bounds of a memory buffer.
The operational impact of CVE-2022-3775 extends beyond simple denial of service conditions, as the memory corruption can potentially lead to system instability and complete bootloader failure. In practical attack scenarios, an adversary could leverage this vulnerability to achieve arbitrary code execution within the bootloader context, particularly when the attacker has control over the boot environment or can influence the input sequences processed by grub2. The attack surface is particularly concerning in environments where grub2 serves as a critical boot component, such as in enterprise systems, embedded devices, or server infrastructure where unauthorized code execution at the bootloader level could provide attackers with persistent access to the target systems. The vulnerability's potential for privilege escalation and system compromise makes it a significant concern for cybersecurity professionals managing boot security.
Mitigation strategies for CVE-2022-3775 should prioritize immediate patch application from upstream grub2 maintainers, as the vulnerability directly affects core bootloader functionality. Organizations should implement comprehensive monitoring for unusual font rendering activities or memory allocation patterns that might indicate exploitation attempts. The remediation process must include thorough validation of all unicode input sequences processed by grub2, with particular attention to glyph dimension constraints and bitmap boundary checks. Security teams should also consider implementing runtime protections such as heap canaries, address space layout randomization, and stack canaries to provide additional defense-in-depth measures against potential exploitation attempts. This vulnerability demonstrates the critical importance of input validation in bootloaders and highlights the need for robust memory safety practices in low-level system components, aligning with ATT&CK technique T1542.001 for bootkit development and T1068 for local privilege escalation through memory corruption vulnerabilities.