CVE-2017-9486 in DPC3939
Summary
by MITRE
The Comcast firmware on Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST) devices allows remote attackers to compute password-of-the-day values via unspecified vectors.
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Analysis
by VulDB Data Team • 11/02/2019
The vulnerability identified as CVE-2017-9486 affects Cisco DPC3939 cable modems running specific Comcast firmware versions, creating a significant security risk that enables remote attackers to derive password-of-the-day values. This flaw represents a critical weakness in the authentication mechanism of these devices, potentially allowing unauthorized access to network management interfaces and services. The vulnerability specifically targets the cryptographic implementation used for generating temporary authentication credentials, which are typically employed for administrative access to the device's web interface. Attackers exploiting this vulnerability can compute valid authentication tokens without requiring legitimate credentials, effectively bypassing the security controls designed to protect the device from unauthorized access.
The technical implementation of this vulnerability stems from weaknesses in the password-of-the-day calculation algorithm within the firmware's authentication subsystem. This flaw allows attackers to predict or reverse-engineer the temporary passwords used for administrative access, which are typically generated using a time-based or deterministic method. The unspecified vectors suggest that the attack could be executed through various network access points, potentially including unauthenticated network connections or through manipulation of network protocols used for device communication. The vulnerability's impact is particularly severe because it undermines the fundamental security model of the device, which relies on time-sensitive authentication tokens to prevent unauthorized access. This weakness creates a persistent backdoor that remains exploitable as long as the vulnerable firmware version is installed, making it a particularly dangerous issue for network administrators managing large deployments of these devices.
The operational impact of CVE-2017-9486 extends beyond simple unauthorized access to encompass potential full network compromise and persistent surveillance capabilities. Attackers who successfully exploit this vulnerability can gain administrative control over the affected cable modems, enabling them to modify network configurations, redirect traffic, or establish persistent access points within the network infrastructure. This capability aligns with attack patterns described in the MITRE ATT&CK framework under the T1078 technique for Valid Accounts, where adversaries leverage compromised credentials to maintain access to systems. The vulnerability also represents a weakness in the NIST SP 800-53 security control families related to authentication and access control, specifically addressing the need for strong authentication mechanisms and the prevention of credential reuse or prediction attacks. Organizations managing these devices face significant risk of network infiltration and potential data exfiltration, as the compromised modems can serve as entry points for broader network attacks.
Mitigation strategies for this vulnerability require immediate firmware updates from Cisco or Comcast, as the flaw exists at the firmware level and cannot be addressed through network configuration changes alone. Network administrators should implement network segmentation to isolate affected devices from critical network segments and monitor for suspicious authentication attempts or unusual network traffic patterns. The vulnerability demonstrates the importance of firmware security and the need for proper cryptographic implementation in embedded systems, aligning with CWE-330 which addresses the use of weak random number generators and predictable cryptographic functions. Organizations should also consider implementing network monitoring solutions that can detect anomalous authentication patterns and establish baseline behaviors for normal device operation to identify potential exploitation attempts. Additionally, the vulnerability highlights the necessity of maintaining current firmware versions and implementing robust patch management processes, particularly for network infrastructure devices that are often overlooked in traditional security monitoring programs.