CVE-2025-60695

Executive Summary

CVE-2025-60695 is a critical stack-based buffer overflow vulnerability discovered in the mtk_dut binary of Linksys E7350 routers running firmware version 1.1.00.032. The flaw resides in the function sub_4045A8, which reads up to 256 bytes from the file /sys/class/net/%s/address into a local buffer and then copies it into a caller-provided buffer a1 using strcpy without boundary checks. Since a1 is often allocated with significantly smaller sizes (20-32 bytes), a local attacker who can control the contents of /sys/class/net/%s/address can trigger a buffer overflow. This can lead to memory corruption, denial of service, or potential arbitrary code execution. The vulnerability is currently unpatched, and no public exploit code or proof-of-concept is available.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in a consumer networking device.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the vulnerability description, a more realistic assessment would be:

• Attack Vector (AV): Local (L) – The attacker must have local access to the device.
• Attack Complexity (AC): Low (L) – The attack requires control over a system file.
• Privileges Required (PR): Low (L) – The attacker needs low-privileged access to the device.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): High (H) – Potential for arbitrary code execution.
• Integrity (I): High (H) – Potential for arbitrary code execution.
• Availability (A): High (H) – Denial of service is possible.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Estimated Score: 7.8 (High)

Threat Level: High. Although local access is required, the potential for arbitrary code execution on a network gateway device poses a significant risk to network security.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the mtk_dut binary, which is likely a diagnostic or utility tool for MediaTek chipsets used in the Linksys E7350 router.

Root Cause: The function sub_4045A8 performs the following operations:

1. Reads up to 256 bytes from the file /sys/class/net/%s/address into a local stack buffer. The %s is replaced with a network interface name (e.g., eth0, wlan0).
2. Copies the contents of this local buffer into a caller-provided buffer a1 using the strcpy function.
3. The caller-provided buffer a1 is often allocated with a size of only 20-32 bytes, which is significantly smaller than the maximum 256 bytes that can be read.

Attack Vector: A local attacker with low privileges on the router can control the contents of /sys/class/net/%s/address by manipulating the network interface's MAC address (e.g., via ip link set dev eth0 address <malicious_data>). When mtk_dut is invoked and processes this interface, the oversized MAC address is copied into the small buffer, causing a stack overflow.

Impact:

• Memory Corruption: Overwriting adjacent stack data.
• Denial of Service (DoS): Crashing the mtk_dut process or the entire system.
• Arbitrary Code Execution: With careful crafting, an attacker could overwrite the return address and execute arbitrary code with the privileges of the mtk_dut process (likely root).

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void sub_4045A8(char *interface, char *a1) {
    char local_buffer[256];
    char path[256];
    snprintf(path, sizeof(path), "/sys/class/net/%s/address", interface);
    FILE *f = fopen(path, "r");
    if (f) {
        fgets(local_buffer, sizeof(local_buffer), f);
        fclose(f);
        // Vulnerable: no size check on a1
        strcpy(a1, local_buffer);
    }
}

Patched Code (Hypothetical):

void sub_4045A8(char *interface, char *a1, size_t a1_size) {
    char local_buffer[256];
    char path[256];
    snprintf(path, sizeof(path), "/sys/class/net/%s/address", interface);
    FILE *f = fopen(path, "r");
    if (f) {
        fgets(local_buffer, sizeof(local_buffer), f);
        fclose(f);
        // Patched: use strncpy with size limit
        strncpy(a1, local_buffer, a1_size - 1);
        a1[a1_size - 1] = '\0';
    }
}

The patch would involve passing the size of the destination buffer and using strncpy or snprintf instead of strcpy.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a Linksys E7350 router running firmware 1.1.00.032.
• Ability to execute commands as a low-privileged user (e.g., via a compromised web interface or SSH).

Exploitation Steps:

1. Identify the vulnerable interface: Determine which network interface is processed by mtk_dut. This may require reverse engineering or trial and error.
2. Craft a malicious MAC address: Create a MAC address string that contains shellcode and padding to overwrite the return address.

   # Example: 256 bytes of 'A' to trigger a crash
   python3 -c "print('AA:BB:CC:DD:EE:FF' + 'A'*240)" > /tmp/mac_payload.txt
   

3. Set the malicious MAC address:

   ip link set dev eth0 address $(cat /tmp/mac_payload.txt)
   

4. Trigger the vulnerability: Run the mtk_dut binary with the appropriate interface argument.

   mtk_dut eth0
   

5. Achieve code execution: If the payload is crafted correctly, the return address will be overwritten, and the shellcode will execute.

Note: No public exploit code is available. This is a theoretical exploitation path.

Blue Team

Detection:

• Monitor for unusual MAC address lengths on network interfaces.
• Monitor for crashes or restarts of the mtk_dut process.
• Monitor for unexpected writes to /sys/class/net/*/address.

Mitigation:

• Restrict access to the router's command line interface.
• Disable unnecessary services like mtk_dut if not required.
• Apply network segmentation to limit local access to the router.

Indicators of Compromise (IOCs)

• File: /sys/class/net/*/address containing data longer than 17 characters (standard MAC address length).
• Process: Crashes or abnormal behavior of the mtk_dut binary.
• Logs: System logs showing mtk_dut segmentation faults or core dumps.
• Network: Unusual MAC addresses on the router's interfaces.

Detection Engineering

YARA Rule

rule CVE_2025_60695_Linksys_E7350_Overflow {
    meta:
        description = "Detects exploitation attempts of CVE-2025-60695 via oversized MAC address in /sys/class/net/*/address"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-60695"
    strings:
        $mac_pattern = /([0-9A-Fa-f]{2}:){5}[0-9A-Fa-f]{2}/
        $long_mac = { ( [0-9A-Fa-f]{2}: ){5} [0-9A-Fa-f]{2} [A-Za-z0-9]{200,} }
    condition:
        $long_mac and filesize > 30
}

Sigma Rule

title: CVE-2025-60695 - Linksys E7350 Stack Buffer Overflow via MAC Address
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects attempts to set an oversized MAC address on a network interface, indicating exploitation of CVE-2025-60695.
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/ip'
        CommandLine|contains: 'link set dev'
        CommandLine|contains: 'address'
        CommandLine|re: '([0-9A-Fa-f]{2}:){5}[0-9A-Fa-f]{2}.{200,}'
    condition: selection
falsepositives:
    - Legitimate use of long MAC addresses (unlikely)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-60695 - Linksys E7350 Stack Buffer Overflow via MAC Address"; flow:to_server; content:"/sys/class/net/"; content:"/address"; within:100; pcre:"/([0-9A-Fa-f]{2}:){5}[0-9A-Fa-f]{2}.{200,}/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict Local Access: Disable SSH, Telnet, and other remote management interfaces if not needed.
2. Monitor Logs: Enable logging and monitor for unusual activity related to mtk_dut.
3. Network Segmentation: Place the router in a segmented network to limit exposure.

Long-Term Fix:

• Vendor Patch: Linksys must release a firmware update that fixes the buffer overflow by using safe string copy functions with proper size checks.
• Workaround: If mtk_dut is not essential, remove or disable the binary.

Valters IT Signature:

This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.