CVE-2024-57261

Executive Summary

CVE-2024-57261 is an integer overflow vulnerability in the request2size macro within the common/dlmalloc.c file of the barebox bootloader. This flaw, related to CVE-2024-57258, allows an attacker to cause a denial of service (DoS) by triggering a memory corruption or crash during memory allocation. The vulnerability is present in all versions of barebox prior to 2025.01.0. While the CVSS score is 7.1 (High), the EPSS score is 0.0%, indicating no active exploitation in the wild at the time of analysis. No public proof-of-concept (PoC) or exploit code is available.

CVSS Breakdown & Threat Level

• CVSS Score: 7.1 (High)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector (AV): Local (L) – The attacker must have local access to the system.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Complete loss of availability (system crash/reboot).

Threat Level: High. Although local access is required, the impact on availability is severe, making it a critical concern for embedded systems and IoT devices using barebox.

Deep Dive & Mechanics

The vulnerability resides in the request2size macro in common/dlmalloc.c. This macro is used to convert a requested memory allocation size into the internal size used by the dlmalloc memory allocator. The macro performs arithmetic operations that can overflow if the requested size is sufficiently large.

Vulnerable Code (Conceptual):

#define request2size(req) \
    (((req) + SIZE_SZ + MALLOC_ALIGN_MASK) & ~MALLOC_ALIGN_MASK)

If req is a very large value (e.g., close to SIZE_MAX), the addition (req) + SIZE_SZ + MALLOC_ALIGN_MASK can overflow, resulting in a small or zero value after masking. This causes the allocator to allocate a much smaller buffer than expected, leading to a heap-based buffer overflow when the caller writes data into the allocated memory.

Attack Scenario: An attacker with local access (e.g., via a compromised user-space process or a malicious boot script) can craft a memory allocation request with a size that triggers the overflow. This can corrupt heap metadata or overwrite adjacent memory, ultimately causing a system crash or denial of service.

Vulnerable vs. Patched Code

Vulnerable (pre-2025.01.0):

#define request2size(req) \
    (((req) + SIZE_SZ + MALLOC_ALIGN_MASK) & ~MALLOC_ALIGN_MASK)

Patched (2025.01.0): The fix involves adding an overflow check before the macro expansion. The patched code ensures that the requested size does not exceed a safe limit, preventing the integer overflow.

#define request2size(req) \
    (__builtin_add_overflow((req), (SIZE_SZ + MALLOC_ALIGN_MASK), &(req)) ? \
     SIZE_MAX : \
     (((req) + SIZE_SZ + MALLOC_ALIGN_MASK) & ~MALLOC_ALIGN_MASK))

The patched version uses __builtin_add_overflow (GCC/Clang built-in) to detect overflow and returns SIZE_MAX (which will cause the allocation to fail) if an overflow is detected.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a barebox-based system (e.g., via serial console or SSH).
• Ability to execute code or trigger memory allocations (e.g., via a custom barebox command or script).

Exploit Concept:

1. Identify a code path that calls malloc() or realloc() with a user-controlled size.
2. Provide a size value that, when processed by request2size, overflows to a small value.
3. Write data larger than the allocated buffer, causing a heap overflow.
4. The overflow corrupts heap metadata or adjacent memory, leading to a crash.

Example (Hypothetical):

// Trigger the overflow
void *ptr = malloc(0xFFFFFFFF); // Large request
if (ptr) {
    memset(ptr, 0x41, 0x1000); // Write more than allocated
}

Note: No public exploit code is available. This is a conceptual demonstration.

Blue Team (Defense)

Detection:

• Monitor for abnormal memory allocation patterns (e.g., extremely large malloc calls).
• Enable kernel or bootloader logging to capture crash dumps.
• Use static analysis tools to identify potential integer overflows in custom barebox modules.

Mitigation:

• Upgrade to barebox 2025.01.0 or later.
• If patching is not possible, restrict local access to the bootloader console.
• Implement input validation for any user-controlled size parameters.

Indicators of Compromise (IOCs)

• System Logs: Entries indicating memory allocation failures or crashes in dlmalloc.
• Crash Dumps: Heap corruption patterns (e.g., 0x41414141 in memory).
• Behavior: Unexpected system reboots or hangs during memory-intensive operations.

Detection Engineering

YARA Rule

rule CVE_2024_57261_barebox_dlmalloc_overflow {
    meta:
        description = "Detects vulnerable request2size macro in barebox dlmalloc.c"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-57261"
    strings:
        $macro = "request2size(req)" ascii wide
        $overflow = "SIZE_SZ + MALLOC_ALIGN_MASK" ascii wide
    condition:
        $macro and $overflow
}

Sigma Rule

title: CVE-2024-57261 - Barebox dlmalloc Integer Overflow
id: 8a3f7c2e-5d1b-4a9e-8c6f-2b3d1e4f5a6c
status: experimental
description: Detects potential exploitation of CVE-2024-57261 via abnormal memory allocation patterns.
author: Valters IT
date: 2025-04-10
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - "malloc: failed to allocate" 
        - "dlmalloc: corruption detected"
        - "kernel: BUG: unable to handle kernel paging request"
    condition: selection
falsepositives:
    - Legitimate memory exhaustion
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-57261 - Barebox dlmalloc Overflow Attempt"; flow:to_server; content:"|FF FF FF FF|"; depth:4; classtype:attempted-dos; sid:1000001; rev:1;)

Note: This Suricata rule is a placeholder. Real-world detection would require protocol-specific analysis.

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade to barebox 2025.01.0 or later.
2. Workaround: If patching is not possible, restrict physical and logical access to the bootloader console.
3. Monitor: Enable detailed logging and monitor for crash events.

Long-Term Measures:

• Implement code reviews and static analysis for integer overflow vulnerabilities.
• Use memory-safe allocators or add bounds checking in custom code.
• Follow secure coding practices (e.g., use __builtin_add_overflow for size calculations).

Valters IT
Securing Digital Frontiers