CVE-2026-23474: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-23474 Overview

A buffer overflow vulnerability has been identified in the Linux kernel's MTD (Memory Technology Device) subsystem, specifically within the RedBoot partition table parser. When CONFIG_FORTIFY_SOURCE=y is enabled alongside a recent compiler that leverages __builtin_dynamic_object_size(), the kernel's fortified string functions detect an out-of-bounds read operation during the partition table parsing process. This results in a kernel warning and subsequent oops, causing a boot crash on affected systems.

The vulnerability stems from improper buffer size calculation when using memcmp() to compare partition names. The allocation size is determined by strlen(), but the subsequent comparison operation reads beyond the allocated buffer boundaries.

Critical Impact

Systems with embedded flash storage using RedBoot partition tables may experience boot failures or kernel panics when the fortify source protection is enabled, potentially leading to denial of service conditions in production environments.

Affected Products

• Linux kernel versions with MTD RedBoot partition table parser enabled
• Systems compiled with CONFIG_FORTIFY_SOURCE=y
• Embedded systems utilizing RedBoot bootloader partition tables

Discovery Timeline

• 2026-04-03 - CVE-2026-23474 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-23474

Vulnerability Analysis

This vulnerability exists in the RedBoot partition table parser within the Linux kernel's MTD subsystem. The issue manifests when the kernel attempts to parse partition table entries during the boot process, specifically when comparing partition names stored in flash memory.

The root of the problem lies in how the names buffer is allocated and subsequently accessed. The allocation is performed using strlen() to determine the size, but the comparison operation using memcmp() attempts to read beyond the allocated buffer boundaries. When CONFIG_FORTIFY_SOURCE is enabled with a compiler supporting __builtin_dynamic_object_size(), this out-of-bounds read is detected, triggering a warning and kernel oops.

The kernel log output demonstrates the issue clearly:

Searching for RedBoot partition table in 50000000.flash at offset 0x7e0000
WARNING: lib/string_helpers.c:1035 at 0xc029e04c, CPU#0: swapper/0/1
memcmp: detected buffer overflow: 15 byte read of buffer size 14

Root Cause

The vulnerability originates from a mismatch between buffer allocation and buffer access in the RedBoot partition table parsing code. The names pointer references the final namelen bytes of the allocation, where namelen could be any arbitrary length. The subsequent memcmp() call attempts to compare more bytes than were actually allocated, resulting in a buffer over-read condition.

This is a classic example of using size-unbounded comparison functions with dynamically allocated buffers where the allocation size is determined by string length but the comparison size is not properly constrained.

Attack Vector

While the immediate impact is a denial of service through boot crashes, the vulnerability could potentially be exploited in scenarios where:

• An attacker can modify partition table data in flash storage
• Crafted partition names could be used to trigger information disclosure through out-of-bounds reads
• Systems with writable flash storage could be targeted to cause persistent boot failures

The fix replaces memcmp() with strcmp(), which naturally operates within string boundaries since the allocation size was calculated using strlen(). This ensures the comparison remains within the allocated buffer bounds.

Detection Methods for CVE-2026-23474

Indicators of Compromise

• Kernel warning messages containing memcmp: detected buffer overflow during boot
• System crashes or panics referencing lib/string_helpers.c and the MTD subsystem
• Boot failures on systems with RedBoot partition tables after enabling CONFIG_FORTIFY_SOURCE

Detection Strategies

• Monitor kernel logs for fortify source warnings related to memcmp buffer overflows
• Check for crashes during MTD partition table parsing at boot time
• Review system boot logs for warnings referencing RedBoot partition table searches

Monitoring Recommendations

• Enable kernel crash dump collection to capture detailed information on affected systems
• Implement automated log analysis for fortify source violation messages
• Monitor embedded device fleets for unexpected boot failures or restart loops

How to Mitigate CVE-2026-23474

Immediate Actions Required

• Apply the kernel patches from the official Linux kernel stable branches
• For systems experiencing boot crashes, temporarily disable CONFIG_FORTIFY_SOURCE until patches can be applied
• Review and update embedded system firmware where RedBoot partition tables are utilized

Patch Information

The Linux kernel maintainers have released patches across multiple stable branches to address this vulnerability. The fix modifies the partition name comparison to use strcmp() instead of memcmp(), ensuring the operation stays within allocated buffer boundaries.

Official patches are available from the following kernel commits:

• Kernel Commit 0b08be5
• Kernel Commit 2025b2d
• Kernel Commit 75a4d8c
• Kernel Commit 8e2f802
• Kernel Commit c4054ad
• Kernel Commit d857021

Workarounds

• Temporarily disable CONFIG_FORTIFY_SOURCE in kernel configuration as a short-term mitigation
• If using custom kernel builds, apply the upstream fix manually by replacing memcmp() with strcmp() in the RedBoot partition parser
• For production systems, schedule maintenance windows to apply kernel updates as soon as patches are available for your distribution

# Check if FORTIFY_SOURCE is enabled in current kernel
zcat /proc/config.gz | grep CONFIG_FORTIFY_SOURCE

# Verify MTD RedBoot parser module status
lsmod | grep mtd
cat /proc/mtd