CVE-2026-86121 in cua-computer-server
Summary
by MITRE • 09/05/2026
Cua computer-server versions before 0.3.42 skip authentication when the CONTAINER_NAME environment variable is unset and bind to all interfaces by default, allowing unauthenticated attackers to execute arbitrary commands. Attackers can reach TCP port 8000 to run shell commands via the run_command endpoint, read and write arbitrary files through file operation endpoints, and access interactive PTY shells without authentication.
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Analysis
by VulDB Data Team • 09/05/2026
The vulnerability in Cua computer-server versions prior to 0.3.42 represents a critical misconfiguration of security controls that fundamentally undermines the integrity and confidentiality of systems running this software. The core technical flaw stems from two distinct but compounding issues: an insecure default binding configuration and a flawed authentication bypass mechanism tied to environment variable handling. By default, the service binds to all network interfaces rather than restricting access to localhost or specific trusted networks. This exposure makes the application accessible to any entity capable of reaching TCP port 8000 on the host machine across the entire network topology, significantly expanding the attack surface beyond what is typically expected for administrative tools.
The authentication bypass occurs specifically when the CONTAINER_NAME environment variable is unset during initialization. In this state, the software fails to enforce mandatory access controls, effectively disabling the requirement for valid credentials before processing incoming requests. This logic error allows unauthenticated actors to interact with sensitive endpoints without providing any form of identity verification. The combination of unrestricted network binding and disabled authentication creates a scenario where remote code execution is trivially achievable by any attacker who can establish a TCP connection to port 8000, regardless of their initial privilege level or location within the network perimeter.
The operational impact of this vulnerability is severe due to the breadth of functionality exposed through these unauthenticated endpoints. Attackers can exploit the run_command endpoint to execute arbitrary shell commands with the privileges of the user running the Cua computer-server process. This capability allows for complete system compromise, including the installation of malware, creation of persistent backdoors, and lateral movement within the network environment. Furthermore, access to file operation endpoints enables attackers to read sensitive configuration files, source code, or credentials stored on disk, as well as write malicious scripts or binaries into executable directories. The availability of interactive PTY shells provides a fully functional command-line interface over HTTP, facilitating complex multi-stage attacks and making forensic analysis more difficult due to the non-standard communication channel used for exploitation.
From a classification perspective, this vulnerability aligns with CWE-287 Improper Authentication, as the system fails to verify identity before granting access. It also relates closely to CWE-601 URL Redirection to Untrusted Site or Bad Endpoint if misconfiguration leads to unintended service exposure, and CWE-434 Unsafe Deserialization if any data passed through these endpoints is processed without validation, though the primary issue remains authentication failure. In terms of offensive security frameworks such as MITRE ATT&CK, this vulnerability facilitates techniques associated with Initial Access via Exploitation of Remote Services and Command and Control using Application Layer Protocol for interactive shell communication. The ability to execute arbitrary commands maps directly to Execution tactics, while file access corresponds to Collection or Exfiltration phases depending on attacker intent.
Mitigation strategies must address both the architectural exposure and the logical flaw immediately. Organizations running Cua computer-server versions before 0.3.42 should upgrade to version 0.3.42 or later where these issues are resolved. Until an upgrade is feasible, it is imperative to restrict network access to TCP port 8000 using firewall rules that limit connectivity to only trusted management networks or specific administrative IP addresses. Additionally, administrators must ensure the CONTAINER_NAME environment variable is properly set during service initialization to enforce authentication checks as intended by the developers. Implementing reverse proxy configurations with strict access control lists can also provide an additional layer of defense by filtering requests before they reach the application backend. Regular auditing of running services and their network bindings should be conducted to prevent similar misconfigurations in other components of the infrastructure.