CVE-2025-7704

Executive Summary

CVE-2025-7704 is a stack-based buffer overflow vulnerability in the Supermicro Baseboard Management Controller (BMC) Insyde SMASH shell program. The flaw allows an unauthenticated attacker to send a specially crafted request to the SMASH shell, potentially leading to arbitrary code execution, denial of service, or privilege escalation within the BMC environment. With a CVSS score of 5.4 (Medium), the vulnerability is remotely exploitable over the network without authentication, but requires low attack complexity and only affects confidentiality, integrity, and availability at a low level. No public exploit code or proof-of-concept is currently available, and no patch has been released by the vendor. The EPSS score of 0.0% indicates very low exploitation activity in the wild at this time.

This vulnerability is specific to Supermicro BMC firmware that includes the Insyde SMASH shell. It is not related to any WordPress plugin or component; the attack surface is the BMC management interface.

Supply Chain & Package Security

Not applicable – this is a firmware-level vulnerability in Supermicro BMC hardware, not an open-source package.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Base Score: 5.4 (Medium)
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Exploit stays within the BMC.
• Confidentiality Impact: Low (C:L) – Limited data exposure.
• Integrity Impact: Low (I:L) – Limited data modification.
• Availability Impact: Low (A:L) – Limited service disruption.

Threat Level: Medium. While the vulnerability is remotely exploitable and unauthenticated, the low impact ratings and lack of active exploitation reduce immediate risk. However, BMC compromise can lead to full server takeover, so patching is critical once available.

Deep Dive & Mechanics

The vulnerability resides in the Insyde SMASH (System Management Architecture for Server Hardware) shell program running on Supermicro BMCs. SMASH is a command-line interface used for server management. The flaw is a classic stack-based buffer overflow (CWE-121) in the SMASH shell’s input handling routine.

When the SMASH shell receives a crafted input string that exceeds the allocated buffer size, it overwrites adjacent stack memory. This can corrupt the return address or other critical data, allowing an attacker to redirect execution flow to arbitrary code. Since the SMASH shell runs with elevated privileges (often root or equivalent within the BMC), successful exploitation can give the attacker full control over the BMC, including the ability to modify firmware, access host system memory, or pivot to the main server.

The vulnerability is triggered by sending a long, specially crafted command or parameter to the SMASH shell over the network (typically via IPMI or web interface). No authentication is required because the SMASH shell may be exposed on the management network without proper access controls.

Vulnerable vs. Patched Code

No patched code is available from the vendor. The vulnerable code is in the Insyde SMASH shell binary within Supermicro BMC firmware. The overflow occurs in a function that copies user input into a fixed-size stack buffer without proper bounds checking.

Vulnerable code snippet (conceptual):

void handle_smash_command(char *input) {
    char buffer[256];
    strcpy(buffer, input);  // No bounds check – overflow if input > 255 bytes
    // ... process command
}

Patched code (expected):

void handle_smash_command(char *input) {
    char buffer[256];
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process command
}

Without an official patch, users must rely on workarounds such as network segmentation and disabling the SMASH shell if possible.

Exploitation & Lab Setup

Red Team

No public exploit code is available. However, a proof-of-concept can be developed by sending a long string to the SMASH shell port (typically port 623 for IPMI or a custom port). The following Python script demonstrates a basic overflow attempt:

import socket

target_ip = "192.168.1.100"
port = 623  # IPMI port, adjust if SMASH uses a different port

# Craft a payload: 300 bytes of 'A' to overflow the buffer
payload = b"A" * 300

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, port))
sock.send(payload)
sock.close()

Note: This is a generic test. Actual exploitation requires precise control of the stack layout and may involve ROP chains or shellcode injection. Use only in authorized lab environments.

Blue Team

To detect exploitation attempts, monitor for abnormally long input strings sent to the SMASH shell or IPMI interface. Network-based detection can identify oversized packets. Host-based detection on the BMC is limited, but logging may show crashes or unexpected reboots.

Detection steps:

1. Enable BMC logging and monitor for SMASH shell crashes.
2. Use network intrusion detection to flag packets with payloads exceeding 256 bytes on management ports.
3. Restrict access to the BMC management interface to trusted IPs only.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Packets to port 623 (IPMI) or custom SMASH port with payloads > 256 bytes.
  • Repeated connection attempts from unknown IPs to the BMC.
• Host IOCs (BMC):
  • Unexpected BMC reboots or crashes.
  • SMASH shell process crashes logged in BMC syslog.
  • Unusual processes or files in the BMC filesystem.
• File IOCs:
  • Modified BMC firmware binaries.
  • Presence of unknown scripts or binaries in /tmp or /var on the BMC.

Detection Engineering

YARA Rule

rule CVE_2025_7704_SMASH_Overflow {
    meta:
        description = "Detects potential stack overflow attempts against Supermicro BMC Insyde SMASH shell"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-7704"
    strings:
        $overflow_pattern = /[A-Za-z0-9]{257,}/  // Matches strings > 256 characters
    condition:
        $overflow_pattern
}

Sigma Rule

title: CVE-2025-7704 SMASH Shell Buffer Overflow Attempt
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects network traffic with long payloads targeting Supermicro BMC SMASH shell
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: suricata
detection:
    selection:
        dest_port:
            - 623
            - 17988  # Example custom SMASH port
        payload_length: >256
    condition: selection
falsepositives:
    - Legitimate long commands (unlikely)
level: high

Suricata Rule

alert tcp any any -> any 623 (msg:"CVE-2025-7704 SMASH Shell Buffer Overflow Attempt"; flow:to_server; content:"|41 41 41|"; offset:0; depth:300; pcre:"/^.{257}/R"; classtype:attempted-admin; sid:1000001; rev:1;)

Note: The Suricata rule uses a simple pattern of repeated 'A' characters (0x41) as a placeholder. Adjust the content match based on actual exploit payloads.

Remediation & Mitigation

1. Patch: No official patch available. Monitor Supermicro and Insyde for updates.
2. Workaround: Disable the SMASH shell if not required. Restrict BMC access to trusted management networks only.
3. Network Segmentation: Place BMCs on a separate VLAN with strict firewall rules.
4. Access Control: Use IPMI authentication and disable anonymous access.
5. Monitoring: Deploy the detection rules above to identify exploitation attempts.
6. Firmware Hardening: If possible, update to the latest BMC firmware version (check vendor for any hotfixes).

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert