CVE-2017-5135 in DPC3928SL
Summary
by MITRE
Certain Technicolor devices have an SNMP access-control bypass, possibly involving an ISP customization in some cases. The Technicolor (formerly Cisco) DPC3928SL with firmware D3928SL-P15-13-A386-c3420r55105-160127a could be reached by any SNMP community string from the Internet; also, you can write in the MIB because it provides write properties, aka Stringbleed. NOTE: the string-bleed/StringBleed-CVE-2017-5135 GitHub repository is not a valid reference as of 2017-04-27; it contains Trojan horse code purported to exploit this vulnerability.
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Analysis
by VulDB Data Team • 08/27/2024
The CVE-2017-5135 vulnerability represents a critical access control flaw in Technicolor network devices, specifically affecting the DPC3928SL modem model with firmware version D3928SL-P15-13-A386-c3420r55105-160127a. This vulnerability stems from improper SNMP (Simple Network Management Protocol) configuration that allows unauthorized remote access to network devices without proper authentication mechanisms. The flaw manifests as an SNMP access-control bypass where any SNMP community string can be used to establish connections from external Internet sources, fundamentally undermining the security posture of affected devices. The vulnerability is particularly concerning because it affects ISP-customized devices, suggesting that the issue may be widespread across networks that utilize Technicolor equipment in residential and small business environments.
The technical implementation of this vulnerability involves the absence of proper authentication controls within the SNMP service configuration, allowing any remote attacker to establish connections using arbitrary community strings. The affected devices provide write access capabilities within their MIB (Management Information Base) structures, making the vulnerability even more dangerous as it permits not only read access but also the ability to modify device configurations. This write access capability transforms what might otherwise be a simple information disclosure vulnerability into a full remote code execution risk. The vulnerability is classified as a CWE-284 (Improper Access Control) issue, which directly relates to the failure to properly enforce access restrictions on network management interfaces. The flaw enables attackers to perform configuration changes, potentially leading to complete device compromise and network infiltration.
The operational impact of CVE-2017-5135 extends beyond simple unauthorized access, as it creates persistent entry points for malicious actors within network infrastructure. When devices are accessible from the Internet with write permissions, attackers can modify routing tables, change network configurations, or even install malicious firmware updates. The vulnerability affects devices that are typically deployed in residential gateway environments, making them prime targets for botnet recruitment and network reconnaissance activities. Organizations using Technicolor devices may experience unauthorized network modifications, data exfiltration, or service disruption. The attack surface is particularly broad since these devices often serve as the primary gateway between internal networks and the Internet, making them ideal targets for lateral movement within compromised networks. The vulnerability's classification under the ATT&CK framework would align with T1059 (Command and Scripting Interpreter) and T1046 (Network Service Scanning) techniques, as attackers could leverage the open SNMP access to discover network topology and execute commands.
Mitigation strategies for CVE-2017-5135 should focus on immediate network segmentation and access control enforcement. Network administrators must disable SNMP access from external interfaces and implement strict access controls using valid community strings with appropriate permissions. The recommended approach includes configuring SNMP to only accept connections from trusted management stations and removing the default or weak community strings that are commonly used for access. Device firmware updates from Technicolor should be applied immediately to address the underlying configuration issues, and network monitoring should be enhanced to detect unauthorized SNMP access attempts. The vulnerability highlights the importance of proper network security configuration management and demonstrates how ISP-customized firmware can introduce unexpected security weaknesses. Organizations should also consider implementing network access control lists to restrict SNMP traffic to authorized management systems only, and establish regular security audits to identify and remediate similar access control vulnerabilities in other network infrastructure components.