CVE-2026-77521 in MaxKB
Summary
by MITRE • 09/21/2026
MaxKB is an open-source AI assistant for enterprise. Prior to version 2.10.5-lts, assistants with a tool, MCP tool, skill, or sub-application use SandboxShellBackend, which exposes an execute shell tool without excluding it and omits execute from interrupt_on, so human approval is not required. Untrusted chat or ingested content can therefore cause command execution; source deployments with MAXKB_SANDBOX disabled run commands directly as the application user, while the official root container's string-based gosu wrapper allowed shell metacharacters to execute outside the intended sandbox. This issue is fixed in version 2.10.5-lts.
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Analysis
by VulDB Data Team • 09/21/2026
The vulnerability identified in MaxKB prior to version 2.10.5-lts represents a critical failure in input validation and access control mechanisms within an enterprise-grade AI assistant platform. As an open-source solution designed for organizational use, the integrity of its execution environment is paramount. The core flaw resides in the SandboxShellBackend component, which serves as the interface for executing shell commands triggered by various features such as tools, MCP tools, skills, or sub-applications. In versions preceding the fix, this backend exposed an execute shell tool without properly restricting its availability to untrusted inputs. Furthermore, the configuration failed to include the execute function in the interrupt_on list, a mechanism typically used to enforce human-in-the-loop approval for sensitive operations. This omission means that automated processes or malicious actors can trigger command execution without any required authorization step, bypassing essential safety controls designed to prevent unauthorized system modifications.
From a technical perspective, this vulnerability allows an attacker who has access to the chat interface or can inject content into ingested documents to achieve arbitrary code execution on the host machine. The severity of the impact is heavily dependent on the deployment configuration. In source deployments where the MAXKB_SANDBOX environment variable is disabled, commands are executed directly under the privileges of the application user account. This provides a direct path for lateral movement or data exfiltration if that user has broad permissions within the local network or file system. Even in containerized environments using the official root image with a string-based gosu wrapper intended to enforce sandboxing, the implementation was flawed. The use of simple string manipulation rather than robust parsing allowed shell metacharacters to break out of the intended sandbox boundaries. This technique effectively neutralizes the containment strategy, allowing commands to run with elevated privileges outside the restricted environment, thereby compromising the isolation guarantees that containerization is supposed to provide.
The operational impact of this vulnerability extends beyond simple command execution. It undermines the trust model of the AI assistant by allowing untrusted inputs to alter system state. An attacker could potentially install backdoors, exfiltrate sensitive data stored on the server, disrupt service availability through resource exhaustion or process termination, or pivot further into internal networks if the application user has network access. This aligns with CWE-78 Improper Neutralization of Special Elements used in an OS Command and CWE-200 Exposure of Sensitive Information to an Unauthorized Actor. The lack of human approval for critical actions also relates to CWE-693 Protection Mechanism Failure, as the intended control mechanism was bypassed due to configuration oversights or implementation errors.
To mitigate this risk, organizations running MaxKB must immediately upgrade to version 2.10.5-lts or later, where these issues have been addressed through improved input sanitization and stricter enforcement of sandbox boundaries. For deployments that cannot be upgraded instantly, it is advisable to disable the use of tools, MCP tools, skills, and sub-applications if they are not strictly necessary for business operations. Additionally, ensuring that MAXKB_SANDBOX remains enabled in source deployments can limit the privilege level of executed commands, although this should not be relied upon as a sole defense given the historical flaws in container wrappers. Implementing network segmentation to restrict the MaxKB application user's access to critical infrastructure and monitoring logs for unusual shell activity are also recommended defensive measures. Regular audits of AI assistant configurations against industry standards such as MITRE ATT&CK technique T1059 Command and Scripting Interpreter can help identify similar misconfigurations in other components of the system.