CVE-2026-39842: Expression Injection in OpenRemote

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.9%, percentile 60: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 60% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes io.openremote:openremote-manager (Maven) <= 1.21.0, fixed in 1.22.0. Check your lockfile, including transitive dependencies.

What it is

OpenRemote is an open-source IoT platform. Versions 1.21.0 and below contain two interrelated expression injection vulnerabilities in the rules engine that allow arbitrary code execution on the server. The JavaScript rules engine executes user-supplied scripts via Nashorn's ScriptEngine.eval() without sandboxing, class filtering, or access restrictions, and the authorization check in RulesResourceImpl only restricts Groovy rules to superusers while leaving JavaScript rules unrestricted for any user with the write:rules role. Additionally, the Groovy rules engine has a GroovyDenyAllFilter security filter that is defined but never registered, as the registration code is commented out, rendering the SandboxTransformer ineffective for superuser-created Groovy rules. A non-superuser attacker with the write:rules role can create JavaScript rulesets that execute with full JVM access, enabling remote code execution as root, arbitrary file read, environment variable theft including database credentials, and complete multi-tenant isolation bypass to access data across all realms. This issue has been fixed in version 1.22.0.

From the GitHub advisory

Summary The OpenRemote IoT platform's rules engine contains two interrelated critical expression injection vulnerabilities that allow an attacker to execute arbitrary code on the server, ultimately achieving full server compromise.

- Unsandboxed Nashorn JavaScript Engine: JavaScript rules are executed via Nashorn's ScriptEngine.eval() with user-supplied script content and no sandboxing, class filtering, or access restrictions. Critically, any non-superuser with the write:rules role can create JavaScript rulesets. - Inactive Groovy Sandbox: The Groovy rules engine has a GroovyDenyAllFilter security filter that is defined but never registered (the registration code is commented out), rendering the SandboxTransformer ineffective. While Groovy rules are restricted to superusers, the absence of sandboxing violates the principle of defense in depth.

Details

Attacker-Controllable Source-to-Sink Paths

There are two non-superuser and two superuser exploitable attack paths from the REST API entry point to final code execution. (JavaScript × Realm/Asset + Groovy × Realm/Asset) The most critical path is detailed below.

Weakness type: CWE-94, CWE-917.

Product: io.openremote:openremote-manager (Maven) · Assigned by: GitHub_M · Published: 2026-04-14

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.91% probability of exploitation activity in the next 30 days; percentile 60.

Timeline

• 2026-04-14 — CVE record published by GitHub_M
• 2026-04-14 — GitHub-reviewed advisory GHSA-7mqr-33rv-p3mp published (critical)
• 2026-04-16 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-7mqr-33rv-p3mp github.com
2. CVE.org record CVE-2026-39842 cve.org
3. NVD entry CVE-2026-39842 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

Critical Maven advisories · Today’s Security Digest