CVE-2017-8415 in DCS-1100
Summary
by MITRE
An issue was discovered on D-Link DCS-1100 and DCS-1130 devices. The device has a custom telnet daemon as a part of the busybox and retrieves the password from the shadow file using the function getspnam at address 0x00053894. Then performs a crypt operation on the password retrieved from the user at address 0x000538E0 and performs a strcmp at address 0x00053908 to check if the password is correct or incorrect. However, the /etc/shadow file is a part of CRAM-FS filesystem which means that the user cannot change the password and hence a hardcoded hash in /etc/shadow is used to match the credentials provided by the user. This is a salted hash of the string "admin" and hence it acts as a password to the device which cannot be changed as the whole filesystem is read only.
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Analysis
by VulDB Data Team • 10/15/2023
The vulnerability identified in D-Link DCS-1100 and DCS-1130 security cameras represents a critical authentication flaw rooted in the device's implementation of the telnet daemon within the busybox framework. This issue stems from a fundamental design decision that creates a permanently hardcoded authentication mechanism, making the device inherently vulnerable to unauthorized access. The affected devices utilize a custom telnet daemon that interfaces with the system's shadow file through the getspnam function located at address 0x00053894, which retrieves password hashes from the /etc/shadow file. The system then performs cryptographic operations on user-provided credentials at address 0x000538E0 and validates the input using strcmp at address 0x00053908, creating a predictable authentication flow that can be easily exploited.
The technical implementation of this vulnerability involves a read-only filesystem constraint that prevents users from modifying the authentication credentials, specifically the /etc/shadow file that contains the password hash. This filesystem is implemented using CRAM-FS which enforces a read-only state, eliminating any possibility of password changes or updates. The system contains a hardcoded salted hash of the string "admin" within the shadow file, creating a fixed authentication mechanism that cannot be altered. This hardcoded approach violates fundamental security principles and creates a persistent backdoor that remains active throughout the device's operational lifecycle. The vulnerability specifically manifests when the telnet daemon attempts to authenticate users, with the system's inability to modify the password hash creating a deterministic authentication process that can be easily reverse-engineered.
The operational impact of this vulnerability extends far beyond simple unauthorized access, as it creates a persistent security risk that affects all devices in the affected product line. The hardcoded "admin" password hash effectively serves as a universal key that can be used to gain administrative control of any D-Link DCS-1100 or DCS-1130 device, regardless of network configuration or physical security measures. This vulnerability directly maps to CWE-255: Credentials Management Issues and CWE-798: Use of Hard-coded Credentials, both of which are classified as high-risk security flaws. The permanent nature of this vulnerability means that even if users attempt to change their passwords through other means, the system's read-only filesystem prevents such modifications, leaving the device perpetually vulnerable. Network administrators cannot rely on standard password management practices, as the authentication mechanism is completely immutable.
The exploitation of this vulnerability follows a straightforward pattern that aligns with ATT&CK technique T1078.004: Valid Accounts - Default Accounts, where attackers can leverage the default hardcoded credentials to establish persistent access to the device. This vulnerability represents a classic case of insecure default configuration that violates security best practices established in frameworks such as NIST SP 800-53 and ISO/IEC 27001. The impact is particularly severe because it affects devices that are commonly deployed in security-sensitive environments such as surveillance systems, where unauthorized access could lead to complete network compromise. The vulnerability also demonstrates poor secure coding practices that could be addressed through proper input validation, dynamic credential management, and appropriate filesystem permissions. Organizations should immediately implement network segmentation and monitoring to detect unauthorized access attempts, while also planning for device replacement or firmware updates when available, as the fundamental flaw resides in the device's architecture rather than in any configuration error.