Atomicorp WAF Research Note: CVE-2026-42796

Arelle < 2.39.10 - Remote Code Execution

Research Notes

This page documents research related to exploit techniques, attack behaviors, testing results, and WAF rule interactions associated with this vulnerability.

Research finding: this note documents observed WAF protections relevant to exploit techniques associated with this vulnerability.

These notes are not intended to represent the full set of vulnerabilities mitigated by Atomicorp products and should not be interpreted as a coverage matrix, certification list, or census of protected CVEs.

Atomicorp WAF protections are primarily designed around attack techniques and exploit behaviors rather than individual vulnerability identifiers. A published research note documents a positive research finding related to that CVE. If a CVE is absent from these notes, no conclusion should be drawn about protection status.

Vulnerability Description

Arelle before 2.39.10 contains an unauthenticated remote code execution vulnerability in the /rest/configure REST endpoint that accepts a plugins query parameter and forwards it to the plugin manager without authentication or authorization. Attackers can supply a URL to a malicious Python file through the plugins parameter, causing the Arelle webserver to download and execute the attacker-controlled code within the Arelle process with its privileges.

Public Vulnerability References

• NVD
• CVE Record

CVE Details

• CVE: CVE-2026-42796
• Name: Arelle < 2.39.10 - Remote Code Execution
• Severity: CRITICAL
• CVSS: 9.2 (Critical)
• CVSS source: VulnCheck CNA
• Vendor: arelle
• Product: arelle
• Latest protected observation: 2026-07-29
• Rule IDs observed: 340162

Test or Research Source

• Source: http/cves/2026/CVE-2026-42796.yaml
• Tags: arelle, cve, cve2026, oast, rce, unauth

Research Note Context

This research note documents exploit-technique analysis associated with this vulnerability and references Atomicorp WAF protections observed during engineering review, testing, or validation activities.

Atomicorp security controls are generally designed to identify and mitigate attack techniques and exploit behaviors rather than individual CVE identifiers. As a result, protections developed for one vulnerability may also apply to related attack variants and future vulnerabilities using similar techniques.

Learn More

Atomicorp develops commercially supported security technologies for web applications, servers, endpoints, workloads, and legacy enterprise platforms.

Organizations interested in protecting systems against exploit techniques associated with vulnerabilities such as this one can learn more about:

• Atomic ModSecurity Rules: commercially maintained WAF rules for ModSecurity deployments, including protections for web attacks, bots, scanners, malware, exploitation attempts, and emerging vulnerability classes.
• Atomic WAF: an enterprise web application firewall with Atomicorp rules, centralized management, reporting, authentication controls, and operational tooling.
• Atomic ModSecurity Integrator: a special licensing option for MSPs, MSSPs, OEMs, VARs, reverse proxy providers, and other integrators who want to incorporate Atomicorp ModSecurity rule technology into their own products or services.
• Atomic OSSEC: an enterprise OSSEC-based intrusion detection, compliance, and security monitoring platform.
• Atomic Protector: workload protection for Linux, web, cloud, data center, and hybrid environments.

For additional information, product evaluations, or technical discussions, visit https://www.atomicorp.com/ or https://modsecurity.io/ .