CVE-2025-70293 in U-Boot
Summary
by MITRE • 08/26/2026
An issue was discovered in Denx U-Boot before 2026.04. An integer overflow vulnerability exists in function ext4fs_get_bgdtable, the size calculation can lead to under allocation and this underallocated buffer will be used in memcpy() which could lead to arbitrary code execution, a denial of service, or other unspecified impacts.
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Analysis
by VulDB Data Team • 08/26/2026
The Denx U-Boot bootloader serves as a critical component in embedded systems, responsible for initializing hardware and loading the operating system kernel into memory before handing over control. As such, any vulnerability within its source code carries significant security implications that extend far beyond the bootloader itself, potentially compromising the entire device lifecycle. The identified integer overflow vulnerability resides specifically within the ext4fs_get_bgdtable function, which is responsible for managing block group descriptors in the Ext4 filesystem structure during boot processes or file system operations initiated by U-Boot. This specific area of code handles low-level data structures that map physical disk blocks to logical addresses, making it a prime target for exploitation if memory management logic fails.
The technical root cause of this vulnerability is an integer overflow occurring during size calculation within the ext4fs_get_bgdtable function. When processing Ext4 metadata, the software calculates the required buffer size based on input parameters derived from filesystem structures. Due to insufficient validation or improper arithmetic handling, a large value can wrap around when added or multiplied, resulting in a significantly smaller calculated size than actually needed. This miscalculation leads directly to heap under-allocation, where the system allocates a memory buffer that is too small to hold the intended data payload. The flaw represents a classic CWE-190 integer overflow condition which cascades into CWE-787 out-of-bounds write when subsequent operations attempt to fill this undersized buffer.
The operational impact of this under-allocation becomes critical during the memcpy operation that follows the allocation step. Because the allocated buffer is smaller than expected, the memcpy function writes data beyond the bounds of the allocated memory region into adjacent heap segments or other sensitive memory areas. This out-of-bounds write corrupts neighboring memory structures and can overwrite control flow data such as return addresses on the stack or function pointers in global offset tables. In a bootloader environment like U-Boot, which often runs with high privileges before full operating system security mechanisms are active, this corruption allows an attacker to achieve arbitrary code execution by redirecting program flow to malicious shellcode placed within the corrupted memory space. Alternatively, if the overwrite corrupts critical state without executing code, it results in a denial of service through immediate crash or undefined behavior during boot sequence.
From a threat modeling perspective, this vulnerability aligns with MITRE ATT&CK techniques related to initial access and privilege escalation via software vulnerabilities. An attacker could exploit this flaw by crafting malicious Ext4 filesystem images containing specially crafted block group descriptors that trigger the integer overflow condition when loaded by U-Boot. This is particularly dangerous in scenarios where devices accept firmware updates or boot from external storage media such as SD cards, USB drives, or network sources without rigorous integrity verification prior to parsing filesystem structures. The ability to execute arbitrary code at this stage means an attacker can persistently modify the bootloader itself, install rootkits that survive OS reinstallation, or extract sensitive cryptographic keys stored in U-Boot environment variables.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements. The primary remediation is upgrading Denx U-Boot to version 2026.04 or later where the integer overflow has been addressed through proper bounds checking and safe arithmetic operations. Developers should implement explicit validation of all size calculations before memory allocation, ensuring that addition or multiplication does not wrap around by using functions like __builtin_add_overflow or similar compiler-provided checks. Additionally, enabling Address Sanitizer during development builds can help detect such heap-based buffer overflows early in the software lifecycle. For deployed systems where immediate patching is not feasible, restricting boot sources to only trusted and verified media reduces the attack surface significantly. Implementing secure boot mechanisms that verify the integrity of filesystem structures before parsing them further mitigates the risk by preventing maliciously crafted images from reaching vulnerable code paths.