CVE-2026-71972 in U-Boot
Summary
by MITRE • 09/30/2026
U-Boot through 2026.10-rc5 contains an out-of-bounds write vulnerability in the video_display_rle8_bitmap function in drivers/video/video_bmp.c. Attackers can supply a crafted RLE8-compressed BMP image to corrupt memory adjacent to the framebuffer and crash the bootloader.
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Analysis
by VulDB Data Team • 09/30/2026
The Universal Boot Loader, commonly known as U-Boot, serves as a critical component in the boot process of many embedded systems and devices running Linux or other operating systems. It is responsible for initializing hardware components and loading the kernel into memory before handing over control to it. Within this context, the video subsystem plays an important role when graphical output is required during early boot stages, such as displaying splash screens or diagnostic information. The vulnerability identified in U-Boot through version 2026.10-rc5 resides specifically within the drivers/video/video_bmp.c source file, affecting the function responsible for rendering RLE8-compressed bitmap images to the display framebuffer. This specific implementation flaw represents a significant security risk because it allows an attacker who can influence or supply boot-time visual assets to execute arbitrary code or cause a denial of service by corrupting adjacent memory regions.
The technical root cause of this vulnerability is an out-of-bounds write condition within the video_display_rle8_bitmap function. RLE8, or Run-Length Encoding 8-bit, is a compression format used in BMP files where each byte represents either a literal pixel value or a run-length pair indicating how many times to repeat the next pixel value. The flaw arises when processing these compressed streams, likely due to insufficient validation of the decompressed data length against the allocated framebuffer size or incorrect pointer arithmetic during the decoding loop. When an attacker provides a crafted RLE8-compressed BMP image with malformed headers or payload structures, the function fails to properly bound-check its write operations. Consequently, it writes pixel data beyond the intended boundaries of the framebuffer buffer into adjacent memory locations. This behavior is classified under CWE-787: Out-of-bounds Write, which describes a situation where software writes data past the end or before the beginning of the intended buffer.
The operational impact of this vulnerability is severe due to the privileged nature of U-Boot execution. Since U-Boot runs with high privileges and controls critical system initialization sequences, corrupting adjacent memory can lead to immediate instability. The most direct consequence described is a crash of the bootloader itself, which results in a denial of service for the target device. However, beyond simple crashes, out-of-bounds writes often allow attackers to overwrite control data such as return addresses, function pointers, or global variables located near the framebuffer in memory layout. This capability can potentially be leveraged for arbitrary code execution during the boot process, allowing an attacker to gain persistent access to the system before the operating system even loads. Such attacks are particularly dangerous because they bypass many runtime security mechanisms that operate at the OS level, as the compromise occurs earlier in the trust chain.
From a threat modeling perspective, this vulnerability aligns with MITRE ATT&CK techniques related to early boot exploitation and memory corruption. Specifically, it relates to T1496: Resource Hijacking if used for denial of service, or more critically, aspects of code execution via buffer overflow patterns often seen in pre-boot environments where Address Space Layout Randomization (ASLR) may not be fully effective or enforced. The attack vector typically requires physical access or the ability to modify boot media, such as a USB drive or SD card containing the malicious image file that U-Boot attempts to display during startup. This makes it relevant for scenarios involving supply chain attacks or tampering with devices before deployment in secure environments.
Mitigation strategies should focus on both immediate patching and long-term defensive coding practices. The primary remediation is to upgrade U-Boot to a version later than 2026.10-rc5, where the vendor has presumably addressed this out-of-bounds write condition by implementing strict bounds checking in the RLE8 decompression logic. Developers should ensure that all input data from external sources, including image files loaded during boot, are validated against expected dimensions and sizes before processing. Additionally, enabling compiler-based security features such as stack canaries or buffer overflow detection tools like AddressSanitizer during development builds can help identify similar issues in the future. For deployed systems where immediate patching is not feasible, restricting physical access to boot media and disabling unnecessary graphical splash screens that rely on external image files can reduce the attack surface significantly.