CVE-2020-5895 in Controller
Summary
by MITRE
On NGINX Controller versions 3.1.0-3.3.0, AVRD uses world-readable and world-writable permissions on its socket, which allows processes or users on the local system to write arbitrary data into the socket. A local system attacker can make AVRD segmentation fault (SIGSEGV) by writing malformed messages to the socket.
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Analysis
by VulDB Data Team • 10/15/2020
The vulnerability identified as CVE-2020-5895 affects NGINX Controller versions 3.1.0 through 3.3.0 and specifically targets the AVRD component responsible for handling socket communications. This flaw represents a critical security oversight in privilege management and file system permissions that fundamentally compromises the integrity of the system's local communication mechanisms. The issue stems from improper permission settings on a critical socket file that governs how the AVRD service communicates with other system components, creating an exploitable attack surface that can be leveraged by local adversaries.
The technical implementation of this vulnerability manifests through the use of world-readable and world-writable permissions on the AVRD socket file, which violates fundamental security principles of least privilege and access control. This misconfiguration allows any user process on the local system to establish connections to the socket and inject arbitrary data into the communication channel. The underlying flaw aligns with CWE-732, which addresses incorrect permissions for critical resources, and demonstrates a clear failure in proper access control implementation. The socket's permissions essentially create a backdoor that bypasses normal authentication and authorization mechanisms that should protect the AVRD service from unauthorized manipulation.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables a local attacker to induce a segmentation fault within the AVRD process through carefully crafted malformed messages. This SIGSEGV condition can result in service disruption, system instability, and potential denial of service scenarios that compromise the availability of the NGINX Controller's monitoring and management capabilities. The attack vector requires local system access but does not necessitate network exposure, making it particularly dangerous in environments where local privilege escalation is possible or where attackers have already gained foothold through other means. This vulnerability can be exploited as part of a broader attack chain to escalate privileges or cause system-wide instability.
Security professionals should implement immediate mitigations including updating to patched versions of NGINX Controller that address the permission configuration issue, manually correcting socket permissions to restrict access to privileged users only, and implementing monitoring for unauthorized socket access attempts. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting local privilege escalation through improper access control mechanisms. Organizations should also conduct comprehensive audits of similar permission configurations across their infrastructure to identify and remediate comparable vulnerabilities that could be exploited in similar ways. The remediation process should include implementing proper file system permissions, utilizing access control lists where appropriate, and ensuring that all system components follow security best practices for socket and file access control.