CVE-2026-52831 in Nuclio
Summary
by MITRE • 09/02/2026
Nuclio is a "Serverless" framework for Real-Time Events and Data Processing. Prior to version 1.16.4, the Nuclio controller builds a curl invocation string for each cron trigger and stores it as the args of a Kubernetes CronJob container (/bin/sh, -c, <command>). Two fields in the trigger specification flow into this string without adequate sanitization: event.headers keys and event.body. This issue has been patched in version 1.16.4.
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Analysis
by VulDB Data Team • 09/02/2026
Nuclio is an open-source serverless framework designed for real-time events and data processing, enabling developers to deploy functions that automatically scale based on incoming traffic or scheduled triggers. A significant security vulnerability was identified within the Nuclio controller prior to version 1.16.4, specifically concerning how it handles cron-triggered tasks. The core of this issue lies in the mechanism used by the Kubernetes CronJob container to execute these scheduled events. Instead of using a safe execution method that separates command arguments from user input, the controller constructs a shell invocation string for each cron trigger. This string is passed as an argument to /bin/sh with the -c flag, which instructs the shell to interpret and execute commands contained within the provided string.
The technical flaw arises because two specific fields from the event specification are injected directly into this command string without adequate sanitization or escaping: the keys of event headers and the content of the event body. Because these inputs flow directly into a shell command execution context, they allow for arbitrary code injection if an attacker can control either the HTTP headers sent to the function endpoint or the payload data processed by the cron-triggered task. This represents a classic Command Injection vulnerability, where untrusted input is used as part of a system-level command without proper validation. The severity of this flaw is amplified by its interaction with Kubernetes infrastructure, meaning that exploitation could potentially lead to container escape or lateral movement within the cluster if the function runs with elevated privileges or accessible shared resources.
From an industry standards perspective, this vulnerability aligns closely with CWE-78 Improper Neutralization of Special Elements used in an OS Command commonly known as OS Command Injection. The failure to sanitize user-supplied input before using it in a shell command is a fundamental security anti-pattern. Furthermore, the exploitation technique maps directly to MITRE ATT&CK tactic T1059 Command and Scripting Interpreter, specifically sub-technique T1059.004 Unix Shell Commands. An attacker could leverage this flaw to execute arbitrary system commands on the underlying node hosting the Kubernetes pod, potentially leading to data exfiltration, denial of service, or further compromise of the cloud environment depending on the permissions assigned to the Nuclio function pods.
The operational impact of this vulnerability is severe for organizations running unpatched versions of Nuclio that utilize cron triggers with user-controllable headers or bodies. Since cron jobs often run with specific service account privileges within Kubernetes, successful exploitation could allow an attacker to read sensitive environment variables, access mounted volumes containing secrets, or execute commands against other services reachable from the pod network. This undermines the isolation guarantees expected in serverless architectures and poses a risk not only to the function itself but potentially to the broader cluster infrastructure if privilege escalation vectors are present.
To mitigate this vulnerability, organizations must upgrade Nuclio to version 1.16.4 or later immediately upon availability. The patch addresses the issue by ensuring that inputs flowing into shell commands are properly sanitized and escaped, preventing arbitrary command execution. In environments where upgrading is not immediately feasible, administrators should implement strict input validation on all event headers and bodies processed by cron-triggered functions to ensure they do not contain shell metacharacters such as semicolons, pipes, or backticks. Additionally, applying the principle of least privilege to Kubernetes ServiceAccounts associated with Nuclio functions can limit the blast radius in case of a successful exploitation attempt. Regular security audits and static analysis tools should be employed to detect similar command injection patterns in custom function code that interacts with system shells.