CVE-2017-15093 in Recursor
Summary
by MITRE
When api-config-dir is set to a non-empty value, which is not the case by default, the API in PowerDNS Recursor 4.x up to and including 4.0.6 and 3.x up to and including 3.7.4 allows an authorized user to update the Recursor's ACL by adding and removing netmasks, and to configure forward zones. It was discovered that the new netmask and IP addresses of forwarded zones were not sufficiently validated, allowing an authenticated user to inject new configuration directives into the Recursor's configuration.
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Analysis
by VulDB Data Team • 02/02/2023
This vulnerability exists in PowerDNS Recursor versions 3.x through 3.7.4 and 4.x through 4.0.6 where the api-config-dir parameter is explicitly configured with a non-empty value. The issue stems from insufficient input validation mechanisms within the API configuration handling system, creating a path for authenticated users to manipulate the recursor's operational parameters. When api-config-dir is properly set, the system enables authorized users to modify Access Control Lists and configure forward zones, but the validation process fails to adequately sanitize the netmask and IP address inputs. The flaw manifests as a configuration injection vulnerability that allows attackers to add or remove network masks and configure forward zones with potentially malicious parameters.
The technical implementation of this vulnerability aligns with CWE-20, which describes improper input validation, and represents a classic case of insufficient sanitization of user-supplied data. An authenticated attacker can exploit this weakness by crafting malicious netmask values or IP addresses that bypass the validation checks, effectively injecting arbitrary configuration directives into the recursor's operational parameters. This creates a scenario where legitimate configuration commands can be corrupted or extended with unauthorized instructions, potentially allowing privilege escalation or denial of service conditions. The vulnerability specifically targets the configuration parsing and validation logic within the API subsystem, where user inputs are processed without adequate security controls to prevent injection attacks.
The operational impact of this vulnerability extends beyond simple configuration manipulation, as it provides a potential pathway for attackers to compromise the DNS resolution infrastructure. An authenticated user could leverage this flaw to redirect DNS queries to malicious servers, create unauthorized forwarding rules, or alter access controls to gain broader system access. The configuration injection capability could be exploited to establish persistent backdoors within the DNS infrastructure or to disrupt legitimate DNS services by modifying forward zone configurations. This vulnerability essentially allows an authenticated attacker to modify critical operational parameters that govern how the recursor handles DNS queries and forwards requests to upstream servers.
Mitigation strategies should focus on implementing robust input validation controls and sanitization mechanisms within the API configuration handling system. Organizations should immediately disable the api-config-dir functionality when not explicitly required, as the vulnerability only manifests when this parameter is configured with a non-empty value. System administrators should also implement strict input validation for all user-supplied parameters, including network masks and IP addresses, using regular expressions or dedicated validation libraries to ensure proper formatting. The implementation of principle of least privilege should be enforced, limiting the number of users with access to the API configuration functionality. Additionally, monitoring and logging of configuration changes should be implemented to detect unauthorized modifications. This vulnerability demonstrates the importance of secure configuration management practices and aligns with ATT&CK technique T1543.003 for creating or modifying system level configuration, making it a critical concern for organizations maintaining DNS infrastructure security.