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CVE-2026-39816 is a high-severity vulnerability in Apache NiFi 2.0.0-M1 through 2.8.0 affecting the optional TinkerpopClientService provided by the nifi-other-graph-services-nar extension. The service is missing a Restricted annotation tied to the Execute Code required permission. TinkerpopClientService supports ByteCode Submission for the Script Submission Type, and in that mode user-supplied input can be processed as Groovy prior to query submission. As a result, in NiFi deployments using fine-grained authorization, an authenticated user who does not have the EXECUTE_CODE permission can still configure and use this service in a way that causes Groovy code to execute on the NiFi server. The flaw is therefore a permission-boundary bypass in an optional graph integration component that exposes an unintended server-side code execution path.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
Repository contains a working proof-of-concept for CVE-2026-39816 against Apache NiFi 2.8.0. The main exploit is pocs/flow_designer_groovy_rce.py, a standalone Python script that authenticates to the NiFi REST API, verifies that the low-privileged user lacks access to restricted scripting processors, then abuses the unrestricted ExecuteGraphQuery/TinkerpopClientService path to execute attacker-supplied Groovy in the NiFi JVM. Its practical payload is a reverse shell callback to the operator, followed by PTY upgrade and interactive terminal handling. This is not merely a detector; it performs end-to-end exploitation and cleanup. Repository structure is split between the exploit and a reproducible lab environment. The setup/ directory provisions a Docker Compose stack with Apache NiFi 2.8.0, OpenLDAP, and a Gremlin server. Supporting files configure LDAP-backed authentication and NiFi authorization, seed two users (admin and flow_designer), patch NiFi properties, and automate startup/teardown. setup.sh also downloads the required graph bundle NARs from Maven Central and configures policies so flow_designer has flow-editing rights but not EXECUTE_CODE, matching the intended bypass scenario. Primary attack vector is web/network-based via authenticated HTTPS access to NiFi's /nifi-api endpoints. The exploit depends on the optional graph bundle being installed and on the attacker having sufficient design permissions to create controller services/processors. Fingerprintable infrastructure includes the NiFi API at /nifi-api/access/token and /flow/process-groups/root, LDAP at ldap://ldap:389, Gremlin at gremlin-server:8182 / ws://gremlin-server:8182/gremlin, Maven Central for NAR downloads, and the reverse-shell callback target host.docker.internal:9998. Overall, this repository is a realistic operational POC demonstrating privilege-boundary bypass leading to arbitrary code execution as the NiFi service account.
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A high-severity Apache NiFi vulnerability caused by a missing restricted annotation for the Execute Code Required Permission, allowing users without EXECUTE_CODE permission to configure TinkerpopClientService to execute Groovy code when the optional graph services extension is installed.
A high-severity authenticated arbitrary code execution vulnerability in Apache NiFi that allows users lacking the EXECUTE_CODE privilege to run Groovy code on the NiFi server via graph query functionality when optional graph-related extensions, including nifi-other-graph-services-nar, are installed.
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