Threat reportVulnerabilityTL-2026-4870
ProjectDiscovery Nuclei Templates April 2026: detection coverage for exploited/KEV-listed CVEs (cPanel & WHM CVE-2026-41940, Langflow CVE-2026-33017, FortiClientEMS) and AI/LLM platforms
ProjectDiscovery Nuclei Templates April 2026 (TL-2026-4870), also tracked as MCPwn (CVE-2026-33032), is a critical-severity software vulnerability, first published 2026-10-31. It has no confirmed attribution, affects cPanel cPanel & WHM / WP Squared, references 10 CVEs (CVE-2026-41940, CVE-2026-33017, CVE-2026-27174), maps to 7 MITRE ATT&CK techniques (T1005, T1059, T1059.006), and is covered by 9 detection rules and 13 indicators of compromise.
- Severity
- CRITICALAssessed severity
- CVEs
- 10Referenced vulnerabilities
- Techniques
- 7MITRE ATT&CK
- Actors
- 0Not attributed
- Detection rules
- 9SPL · KQL · Sigma
- IOCs
- 13Indicators of compromise
Key facts for TL-2026-4870
- Threat ID
- TL-2026-4870
- Also known as
- MCPwn (CVE-2026-33032)
- Severity
- CRITICAL
- Status
- ACTIVE
- Category
- VULNERABILITY
- First published
- Last reviewed
- Attribution confidence
- LOW
- Motivation
- UNKNOWN
- Target sectors
- technology, web hosting, government administration, telecoms, ai ml
- Target regions
- Global
- Detection rules
- 9
- Indicators of compromise
- 13
Malware and tooling in ProjectDiscovery Nuclei Templates April 2026
Malware and tooling: Interactsh, Nuclei
How ProjectDiscovery Nuclei Templates April 2026 works
ProjectDiscovery's April 2026 Nuclei release summary (v10.4.2 and v10.4.3) adds 226 templates covering 123 CVEs, including 10 exploited/KEV-listed CVEs in cPanel & WHM, Langflow, MajorDoMo, SmarterMail, Nginx UI, LMDeploy and FortiClient EMS. It also expands AI/LLM attack-surface coverage (Langflow, Flowise, Marimo, LiteLLM, ComfyUI and others).
ProjectDiscovery published its April 2026 Nuclei Templates summary on 2026-05-12. Two releases are covered: v10.4.2 (2026-04-15; 121 templates, 61 CVEs) and v10.4.3 (2026-05-05; 105 templates, 62 CVEs), for 226 new templates, 123 CVEs and 27 first-time contributors. This is a detection-coverage roundup rather than a single vulnerability report, so the value to defenders is the list of exploited CVEs that now have open-source detection templates.
The source lists ten exploited/KEV-listed CVEs: CVE-2026-41940 (cPanel & WHM session-file CRLF injection authentication bypass), CVE-2026-33017 (Langflow unauthenticated RCE, versions before 1.9.0), CVE-2026-27174 (MajorDoMo unauthenticated RCE), CVE-2026-24423 (SmarterMail RCE), CVE-2026-33032 (Nginx UI broken access control), CVE-2026-33626 (LMDeploy SSRF), CVE-2026-3844 (Breeze arbitrary file upload, 2.4.4 and earlier), CVE-2025-13390 (WP Directory Kit authentication bypass, 1.4.4 and earlier), CVE-2026-21643 (FortiClientEMS SQL injection, 7.4.4) and CVE-2026-35616 (FortiClient EMS authentication bypass). It also highlights 22 further critical/high issues, including Apache ActiveMQ (CVE-2026-34197, CVE-2026-40466), OpenAM (CVE-2026-33439), FortiSandbox (CVE-2026-39808), NocoBase (CVE-2026-34156), Marimo (CVE-2026-39987), Flowise (CVE-2025-59528), Cockpit (CVE-2026-4631), Cisco Secure Firewall Management Center (CVE-2026-20079) and Progress ShareFile (CVE-2026-2699).
Supplementary sources add mechanics for several of the listed CVEs. cPanel & WHM CVE-2026-41940 (CVSS 9.8, CWE-93) abuses the whostmgrsession cookie and raw CRLF characters injected via a basic authorization header so that unsanitized session files are written with attacker-chosen properties such as user=root; suspected zero-day exploitation began 2026-02-23, the patch shipped 2026-04-28 and CISA added it to KEV on 2026-04-30, with about 1.5 million exposed instances reported. Langflow CVE-2026-33017 (CVSS 9.8; CWE-94/95/306) is reachable via POST /api/v1/build_public_tmp/{flow_id}/flow, where an attacker-supplied data parameter replaces the stored flow and its Python code runs through exec() during graph construction; exploitation was seen about 20 hours after the 2026-03-17 advisory, the CVE was added to KEV on 2026-03-25, and attackers harvested environment variables, .env files and SQLite databases for AI-provider and cloud keys. Nginx UI CVE-2026-33032 ("MCPwn", CVSS 9.8) stems from the /mcp_message MCP endpoint lacking the auth middleware; it is fixed in 2.3.4. LMDeploy CVE-2026-33626 is an SSRF in the vision-language load_image() function (0.12.0 and earlier, fixed in 0.12.3) exploited about 12.5 hours after its 2026-04-21 advisory, including retrieval of AWS instance metadata credentials. SmarterMail CVE-2026-24423 (CVSS 9.8) is unauthenticated RCE via the ConnectToHub API in builds before 9511 and is used in ransomware attacks. FortiClient EMS CVE-2026-35616 affects 7.4.5/7.4.6 and was added to KEV on 2026-04-06. MajorDoMo CVE-2026-27174 (CVSS 10) combines a missing exit after redirect in the admin panel with eval() in the PHP console.
The ProjectDiscovery source supplies no CVSS scores, IOCs or attribution for the roundup, so no threat actor is attributed. Scoring is left null at the roundup level; severity is CRITICAL because of the KEV-listed, actively exploited designation.
MITRE ATT&CK techniques used in TL-2026-4870
Collection
Execution
T1059 Command and Scripting Interpreter; T1059.006 Command and Scripting Interpreter: Python
Initial Access
T1190 Exploit Public-Facing Application
Credential Access
T1552.001 Unsecured Credentials: Credentials In Files; T1552.005 Unsecured Credentials: Cloud Instance Metadata API
Reconnaissance
Affected products and versions in ProjectDiscovery Nuclei Templates April 2026
- cPanel — cPanel & WHM / WP Squared
Vulnerable versions: 11.40 and later prior to fixed builds; WP Squared < 136.1.7
Fixed in: 11.86.0.41; 11.110.0.97; 11.118.0.63; 11.126.0.54; 11.130.0.19; 11.132.0.29; 11.134.0.20; 11.136.0.5; WP Squared 136.1.7 - Langflow — Langflow
Vulnerable versions: <= 1.8.2; < 1.9.0
Fixed in: 1.9.0 - Nginx UI — nginx-ui
Vulnerable versions: < 2.3.4
Fixed in: 2.3.4 - InternLM — LMDeploy
Vulnerable versions: <= 0.12.0
Fixed in: 0.12.3 - SmarterTools — SmarterMail
Vulnerable versions: < build 9511
Fixed in: build 9511 - Fortinet — FortiClient EMS
Vulnerable versions: 7.4.4 (CVE-2026-21643); 7.4.5; 7.4.6 (CVE-2026-35616)
Fixed in: 7.4.7 (CVE-2026-35616) - MajorDoMo — MajorDoMo
Vulnerable versions: unspecified in source - Breeze — Breeze
Vulnerable versions: <= 2.4.4 - WP Directory Kit — WP Directory Kit
Vulnerable versions: <= 1.4.4
Remediation for ProjectDiscovery Nuclei Templates April 2026
Patches
- cPanel & WHM: 11.86.0.41, 11.110.0.97, 11.118.0.63, 11.126.0.54, 11.130.0.19, 11.132.0.29, 11.134.0.20, 11.136.0.5; WP Squared 136.1.7
- Langflow 1.9.0 or later
- Nginx UI 2.3.4 or later
- LMDeploy 0.12.3 or later
- SmarterMail build 9511 or later
- FortiClient EMS 7.4.7 (fix for CVE-2026-35616)
Immediate actions
- Run the April 2026 Nuclei templates (v10.4.2/v10.4.3) against internet-facing assets to find exposed cPanel & WHM, Langflow, Nginx UI, LMDeploy, SmarterMail, MajorDoMo and FortiClient EMS instances
- Remove FortiClient EMS, cPanel/WHM, Nginx UI and AI/LLM management interfaces from direct internet exposure
- Review web and session logs for CRLF sequences in Authorization headers and for requests to /api/v1/build_public_tmp/, /mcp_message and ConnectToHub
- Rotate API keys, cloud credentials and secrets stored on any exposed Langflow, LMDeploy or similar AI hosts
Workarounds
- Restrict access to management panels and AI platform endpoints by IP allow-list or VPN until patched
- Block outbound requests to known OAST/Interactsh callback domains where not needed
Longer-term hardening
- Track CISA KEV additions and prioritize patching of listed CVEs within the federal due dates
- Enforce authentication and network segmentation for AI/LLM platforms, MCP endpoints and vector databases
- Block egress to cloud instance metadata from application workloads and require IMDSv2
CVEs associated with ProjectDiscovery Nuclei Templates April 2026
CVE-2026-41940, CVE-2026-33017, CVE-2026-27174, CVE-2026-24423, CVE-2026-33032, CVE-2026-33626, CVE-2026-3844, CVE-2025-13390, CVE-2026-21643, CVE-2026-35616
Weaknesses (CWE) in ProjectDiscovery Nuclei Templates April 2026
Timeline of ProjectDiscovery Nuclei Templates April 2026
- CISA adds SmarterMail CVE-2026-24423 to KEV, marked as used in ransomware campaigns; federal deadline 2026-02-26
- Suspected zero-day exploitation of cPanel & WHM CVE-2026-41940 begins, per hosting-provider reporting
- Advisory published for Langflow CVE-2026-33017 (GHSA-vwmf-pq79-vjvx)
- First in-the-wild exploitation of Langflow CVE-2026-33017 observed on a honeypot about 20 hours after disclosure
- CISA adds Langflow CVE-2026-33017 to KEV; federal deadline 2026-04-08
- CISA adds FortiClient EMS CVE-2026-35616 to KEV; federal deadline 2026-04-09
- Nuclei Templates v10.4.2 released: 121 templates covering 61 CVEs
- LMDeploy CVE-2026-33626 advisory published; first exploitation attempt detected about 12.5 hours later
- cPanel releases fixes for CVE-2026-41940
- CISA adds cPanel & WHM CVE-2026-41940 to KEV; Nuclei check released
- Nuclei Templates v10.4.3 released: 105 templates covering 62 CVEs
- ProjectDiscovery publishes the April 2026 Nuclei templates summary (226 templates, 123 CVEs)
Sources cited for ProjectDiscovery Nuclei Templates April 2026
- Nuclei Templates - April 2026 (ProjectDiscovery)
- Rapid7: CVE-2026-41940 cPanel & WHM Authentication Bypass
- SecurityWeek: Critical cPanel & WHM Vulnerability Exploited as Zero-Day for Months
- Help Net Security: cPanel zero-day exploited for months before patch release (CVE-2026-41940)
- CSA Research Note: CVE-2026-33017 Unauthenticated RCE in Langflow AI Pipelines
- CSA Research Note: LMDeploy SSRF AI Inference Exploitation (CVE-2026-33626)
- The Hacker News: LMDeploy CVE-2026-33626 flaw exploited
- NVD: CVE-2026-33032 (nginx-ui MCPwn)
- SecurityWeek: Exploited Vulnerability Exposes Nginx Servers to Hacking
- Help Net Security: Ransomware attackers are exploiting critical SmarterMail vulnerability (CVE-2026-24423)
- Resecurity: Critical MajorDoMo RCE CVE-2026-27174 Analysis
- Nopal Cyber Threat Hunting Advisory: FortiClient EMS CVE-2026-35616
Detection coverage for TL-2026-4870
As of 2026-10-31, Threadlinqs Intelligence publishes 9 detection rule(s) for TL-2026-4870 across Splunk SPL, Microsoft KQL and Sigma, covering 13 indicator(s) of compromise. The whole corpus is readable without an account; a free account unlocks full detection query text in Splunk SPL, Microsoft KQL and Sigma; paid tiers add raw indicator values, correlation and the MCP server. Threadlinqs MCP server · View plans.