CVE-2025-70293 Overview
CVE-2025-70293 is an integer overflow vulnerability in Denx U-Boot versions prior to 2026.04. The flaw resides in the ext4fs_get_bgdtable function, where a size calculation can overflow and produce an undersized buffer allocation. The undersized buffer is then passed to memcpy(), resulting in a heap buffer overflow. Exploitation can lead to arbitrary code execution, denial of service, or other unspecified impacts on affected bootloaders.
Critical Impact
An attacker able to influence ext4 filesystem metadata processed by U-Boot can trigger memory corruption during boot, potentially compromising firmware integrity and device availability.
Affected Products
- Denx U-Boot versions prior to 2026.04
- Embedded systems and devices that ship U-Boot as their bootloader
- Firmware images that parse ext4 filesystems via U-Boot at boot time
Discovery Timeline
- 2026-08-26 - CVE CVE-2025-70293 published to NVD
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2025-70293
Vulnerability Analysis
The defect is an integer overflow [CWE-190] in the ext4fs_get_bgdtable function of U-Boot's ext4 filesystem driver. The function computes the size of the ext4 block group descriptor table before allocating a buffer to hold it. When attacker-controlled filesystem parameters push the multiplication beyond the width of the underlying integer type, the computed size wraps to a smaller value. U-Boot allocates that undersized buffer and then copies the actual descriptor data into it with memcpy(), writing past the end of the allocation.
The write overflows adjacent heap memory used by U-Boot during early boot. Because U-Boot executes with full memory privileges before any operating system loads, corruption in this region can redirect control flow or halt the boot process entirely.
Root Cause
The root cause is missing validation of the arithmetic used to size the block group descriptor table allocation. Values sourced from the ext4 superblock, such as the number of block groups and descriptor size, are multiplied without a prior bounds check or use of overflow-safe arithmetic. The resulting wrapped value silently under-allocates the destination buffer.
Attack Vector
An attacker who can present a crafted ext4 filesystem to U-Boot triggers the flaw. Realistic delivery channels include malicious removable media, tampered boot partitions on eMMC or SD storage, network-loaded root filesystems, and supply chain modifications to firmware images. The vulnerability is exploited before the operating system loads, so standard OS-level protections are not in effect. See the GitHub Gist Code Snippet referenced in the advisory for technical detail on the vulnerable code path.
No verified public exploit code is available at this time.
Detection Methods for CVE-2025-70293
Indicators of Compromise
- Unexpected U-Boot boot failures, resets, or hangs while probing ext4 partitions
- Serial console output showing memory faults or aborted filesystem reads during early boot
- Unauthorized modifications to boot partitions, ext4 superblock fields, or firmware update payloads
Detection Strategies
- Inventory device fleets to identify units running U-Boot builds older than 2026.04
- Validate cryptographic signatures on firmware images and boot media before deployment
- Inspect ext4 superblock values on boot media for out-of-range block group counts or descriptor sizes
Monitoring Recommendations
- Capture and centrally log U-Boot serial console output from production and lab devices
- Alert on repeated boot failures or watchdog resets that correlate with storage or firmware changes
- Track firmware version telemetry from managed devices to confirm patch adoption
How to Mitigate CVE-2025-70293
Immediate Actions Required
- Upgrade U-Boot to version 2026.04 or later on all affected devices and reference designs
- Restrict physical and logical access to boot media, including SD cards, eMMC, and USB devices
- Enforce verified boot and signed firmware to reject tampered ext4 images before U-Boot parses them
Patch Information
The vulnerability is fixed in Denx U-Boot 2026.04. Downstream vendors that maintain forks of U-Boot for their platforms should backport the fix and issue firmware updates. Consult the U-Boot Project Homepage and the Denx Homepage for release information and vendor guidance.
Workarounds
- Disable ext4 filesystem support in U-Boot builds where it is not required
- Load kernels and initramfs from read-only, integrity-verified sources instead of writable ext4 partitions
- Enable secure boot and hardware root of trust to prevent unauthorized boot media from being processed
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
