In early 2024, a subtle but critical security issue was identified and patched in the Linux kernel’s boot process. Tracked as CVE-2024-26988, this vulnerability involved a potential memory overflow when processing boot command line arguments. This article breaks down what caused the bug, its risk, and how developers fixed it—with simple code snippets and clear explanations.

What is CVE-2024-26988?

The Linux kernel receives various command-line arguments during the boot process. These arguments are used to control kernel boot options like “root device”, logging levels, etc.

In vulnerable Linux kernels, the code in init/main.c tried to combine two strings: extra_command_line and command_line, and store both in a new heap-allocated buffer, static_command_line.

The bug:
The allocation was the wrong size. It was based on the length of boot_command_line, not command_line. If command_line was longer, the buffer would be too small, and copying data into it would cause a memory overflow—potentially letting attackers overwrite heap data.

Here’s a simplified version of the buggy code before the patch

// Old buggy allocation code:

size_t xlen = strlen(extra_command_line);
// 'boot_command_line' length used, but wrong:
static_command_line = memblock_alloc(xlen + strlen(boot_command_line) + 1, SMP_CACHE_BYTES);

strcpy(static_command_line, extra_command_line);     // Copy extra arguments
strcat(static_command_line, command_line);           // Copy actual command line

Problem:
If strlen(command_line) > strlen(boot_command_line), the buffer isn’t big enough, causing overflow as soon as strcat runs.

Fixed code snippet

// New fixed allocation:
size_t xlen = strlen(extra_command_line);
static_command_line = memblock_alloc(xlen + strlen(command_line) + 1, SMP_CACHE_BYTES);

strcpy(static_command_line, extra_command_line);
strcat(static_command_line, command_line);

Now, the buffer is always large enough—even if command_line is longer than boot_command_line. No more overflow.

Why Does This Matter?

Overflow vulnerabilities in kernel code are dangerous. If an attacker can influence kernel boot arguments (sometimes possible in VM or server environments), this bug could allow them to:

In rare cases, escalate privileges or bypass kernel security.

While this bug is early in the boot process (limiting attack scenarios), it's a classic example of how small mistakes in length calculations can have big consequences in low-level C code.

References and Resources

- 🔗 Linux kernel commit fixing CVE-2024-26988 (see entry: “init/main.c: Fix potential static_command_line memory overflow”)
- 🔗 NVD CVE-2024-26988 entry
- 🔗 Original problematic commit, f5c731ac73e
- 📖 Linux kernel documentation—kernel parameters

Exploit Details (How Might Attackers Abuse This?)

Direct exploitation is tricky because most systems lock down who can add kernel command-line arguments.

Possible exploit scenario:
- In shared hosting or public clouds, if a privileged attacker can pass long boot arguments (command_line), and if kernel protection like KASLR is disabled, they might exploit this overflow.
- Could lead to arbitrary kernel memory overwrite during boot, possibly allowing privilege escalation before most security features are loaded.

No public exploits are currently available, but the issue demonstrates the danger of off-by-one and buffer sizing mistakes in the kernel.

Conclusion

CVE-2024-26988 was a serious bug, even if hard to trigger for most users. It highlights the need for attention to detail when handling string lengths and memory in system programming, especially in critical code like the Linux kernel boot sequence.

Recommendation:
- All Linux users, especially those maintaining custom kernels, should update to a version with this fix.

Stay safe and keep your systems updated!

*This article is exclusive, uses plain terms, and explains the technical details for anyone interested in Linux security. If you have kernel-level access or manage boot parameters, double-check your systems for this patch!*

Timeline

Published on: 05/01/2024 06:15:16 UTC
Last modified on: 11/04/2025 18:16:05 UTC