Description

A flaw has been found in D-Link DCS-930L B1.08B4. This impacts the function mpfd_decode of the file bootloader_region.bin of the component Emergency HTTP Recovery Server. Executing a manipulation of the argument firmware can lead to improper verification of cryptographic signature. The attack may be performed from remote. The exploit has been published and may be used.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.6",
  "pubDate": "2026-10-13T06:16:50.090Z",
  "pubdate": "2026-10-13T06:16:50.090Z",
  "executiveSummary": "A critical security vulnerability has been identified in the Emergency HTTP Recovery Server component of the D-Link DCS-930L (version B1.08B4). The flaw resides in the mpfd_decode function within bootloader_region.bin, which fails to correctly perform cryptographic signature verification during the firmware update process.\nThis vulnerability is classified as a signature bypass issue, allowing an unauthenticated remote attacker to provide a malicious firmware image that the system will accept as authentic. The risk implications are severe, as successful exploitation enables arbitrary code execution at the bootloader or system level, potentially leading to full device compromise, persistence, or complete loss of control.\nThe attack vector is remote, requiring no prior authentication. Given that functional exploit code has been publicly disclosed, the vulnerability is highly accessible to threat actors. Organizations utilizing this device should treat this as a high-priority incident due to the nature of the recovery server's privileged position in the boot sequence.",
  "technicalDetails": "The vulnerability originates within the Emergency HTTP Recovery Server, a specialized component designed to allow for system restoration via the web interface. The core of the issue is located in the mpfd_decode function of the binary bootloader_region.bin, which is responsible for parsing and processing incoming firmware update payloads.\nThe root cause is an improper verification mechanism for the cryptographic signatures accompanying firmware updates. During the decoding of the firmware multipart data, the function fails to adequately validate the integrity or the authenticity of the supplied firmware blob before proceeding with the extraction or update process. This effectively treats a malicious, unsigned, or improperly signed binary as a trusted firmware image.\nThe attack flow proceeds as follows: First, an attacker interacts with the Emergency HTTP Recovery Server over the network, typically via an HTTP POST request targeting the firmware update interface. The attacker crafts a payload that manipulates the 'firmware' argument. Because the mpfd_decode routine does not enforce cryptographically sound signature checks, the logic proceeds to write the malicious binary data into the target memory regions or flash storage without verifying if the firmware originated from a legitimate source.\nUpon successful injection of the arbitrary firmware, the device proceeds to install or execute the malicious code. As the component resides within the bootloader-related logic, the payload can execute with high privileges, potentially overriding existing security controls, establishing a persistent backdoor, or reconfiguring the device environment. The exploit leverages the public availability of the vulnerability, utilizing existing methods to bypass the insufficient security checks.\nThe lack of authentication requirements allows remote actors to initiate this process without needing administrative credentials. Because the Emergency HTTP Recovery Server is specifically exposed to facilitate recovery operations, it remains a primary target for exploitation when the device is reachable via a network. This flaw represents a failure in the secure boot chain implementation, where the trust anchor for firmware updates is circumvented by the faulty decoding logic."
}