Atomicorp WAF Research Note: CVE-2026-41940

cPanel & WHM - Authentication Bypass via Session-File CRLF Injection

CVE Details

• Protection status: Understanding Atomicorp WAF Protection Status
• CVE: CVE-2026-41940
• Name: cPanel & WHM - Authentication Bypass via Session-File CRLF Injection
• Severity: Critical
• CVSS: 9.3 (v4.0) (Critical)
• CVSS version: 4.0
• CVSS source: N/A
• CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
  • Attack vector: Network
  • Attack complexity: Low
  • Attack requirements: None
  • Privileges required: None
  • User interaction: None
  • Vulnerable-system confidentiality: High
  • Vulnerable-system integrity: High
  • Vulnerable-system availability: High
  • Subsequent-system confidentiality: None
  • Subsequent-system integrity: None
  • Subsequent-system availability: None
  • Scope: X
• CWE: CWE-306 — Missing Authentication for Critical Function
• Related CAPEC attack patterns (via MITRE CWE relationships): CAPEC-12 (opens in a new tab) , CAPEC-166 (opens in a new tab) , CAPEC-216 (opens in a new tab) , CAPEC-36 (opens in a new tab) , CAPEC-62 (opens in a new tab)
• Vendor: cpanel
• Vulnerable product: cpanel
• CVE published: 2026-04-29
• CVE last modified: 2026-06-17
• Affected versions (NVD configurations):
  • cpanel: >= 11.40, < 86.0.41
  • cpanel: >= 88.0.0, < 110.0.97
  • cpanel: >= 112.0.0, < 118.0.63
  • cpanel: >= 120.0.0, < 124.0.35
  • cpanel: >= 126.0.1, < 126.0.54
  • cpanel: >= 128.0.0, < 130.0.19
  • cpanel: >= 132.0.0, < 132.0.29
  • cpanel: >= 134.0.0, < 134.0.20
  • cpanel: >= 136.0.0, < 136.0.5
  • whm: >= 11.40, < 86.0.41
  • whm: >= 88.0.0, < 110.0.97
  • whm: >= 112.0.0, < 118.0.63
  • whm: >= 120.0.0, < 124.0.35
  • whm: >= 126.0.1, < 126.0.54
  • whm: >= 128.0.0, < 130.0.19
  • whm: >= 132.0.0, < 132.0.29
  • whm: >= 134.0.0, < 134.0.20
  • whm: >= 136.0.0, < 136.0.5
  • wp squared: < 136.1.7
• EPSS: 0.9853; 99.9th percentile (FIRST (opens in a new tab) )
• CISA KEV: Listed (added 2026-04-30)
  • Known ransomware campaign use: Known
• Latest Update: 2026-08-06
• Selected Rule IDs observed: 377364
• Matching rules: 1; rules with blocking actions: 0
• Would-block Rule IDs: N/A

Vulnerability Description

cPanel and WHM versions after 11.40 contain an authentication bypass vulnerability in the login flow that allows unauthenticated remote attackers to gain unauthorized access to the control panel.

Recommended Actions

1. Maintain the observed Atomicorp detections. Keep your Atomicorp commercial rules current and confirm that the selected observed rules (377364 ) have not been locally disabled. Atomicorp commercial rules are enabled by default. If you use Atomic WAF, review the applicable policy and rule settings. These observations are detection-only; review the resulting events and do not assume they block exploitation.

2. Apply the vendor’s remediation. WAF protection is defense in depth and does not replace upgrading or following the affected vendor’s guidance.

   • Affected versions: WebPros cPanel versions earlier than 11.86.0.41.
   • Affected versions: WebPros cPanel versions earlier than 11.94.0.28.
   • Affected versions: WebPros cPanel versions earlier than 11.102.0.39.
   • Affected versions: WebPros cPanel versions earlier than 11.110.0.97.
   • Affected versions: WebPros cPanel versions earlier than 11.118.0.63.
   • Affected versions: WebPros cPanel versions earlier than 11.124.0.35.
   • Affected versions: WebPros cPanel versions earlier than 11.126.0.54.
   • Affected versions: WebPros cPanel versions earlier than 11.130.0.19.
   • Affected versions: WebPros cPanel versions earlier than 11.132.0.29.
   • Affected versions: WebPros cPanel versions earlier than 11.134.0.20.
   • Affected versions: WebPros cPanel versions earlier than 11.136.0.5.
   • Versions reported unaffected: WebPros WP Squared version 11.136.1.7.
   • Affected versions: WebPros WHM versions earlier than 11.86.0.41.
   • Affected versions: WebPros WHM versions earlier than 11.94.0.28.
   • Affected versions: WebPros WHM versions earlier than 11.102.0.39.
   • Affected versions: WebPros WHM versions earlier than 11.110.0.97.
   • Affected versions: WebPros WHM versions earlier than 11.118.0.63.
   • Affected versions: WebPros WHM versions earlier than 11.124.0.35.
   • Affected versions: WebPros WHM versions earlier than 11.126.0.54.
   • Affected versions: WebPros WHM versions earlier than 11.130.0.19.
   • Affected versions: WebPros WHM versions earlier than 11.132.0.29.
   • Affected versions: WebPros WHM versions earlier than 11.134.0.20.
   • Affected versions: WebPros WHM versions earlier than 11.136.0.5.
   • The CVE record does not include written upgrade or workaround instructions, but it does publish the following patch or mitigation reference:
     • Patch or mitigation information (opens in a new tab)
     • Patch or mitigation information (opens in a new tab)
   • CISA KEV required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   • CISA KEV federal remediation due date: 2026-05-03

3. Validate after changes. Confirm rule updates are current, review WAF events for the affected application, and test application behavior after vendor upgrades, mitigations, or local policy changes.

Research Notes

Atomicorp WAF protections are designed around attack techniques and exploit behaviors, allowing existing protections to apply across multiple vulnerabilities without requiring a unique rule for every CVE.

Public Vulnerability References

• NVD (opens in a new tab)
• CVE Record (opens in a new tab)
• Patch or mitigation: https://docs.cpanel.net/release-notes/release-notes (opens in a new tab)
• Patch or mitigation: https://docs.wpsquared.com/changelogs/versions/changelog/#13617 (opens in a new tab)
• Vendor advisory: https://support.cpanel.net/hc/en-us/articles/40073787579671-cPanel-WHM-Security-Update-04-28-2026 (opens in a new tab)
• Exploit or technical research: https://www.namecheap.com/status-updates/ongoing-critical-security-vulnerability-in-cpanel-april-28-2026 (opens in a new tab)
• Exploit or technical research: https://www.vulncheck.com/advisories/cpanel-and-whm-authentication-bypass-via-login-flow (opens in a new tab)
• Exploit or technical research: https://labs.watchtowr.com/the-internet-is-falling-down-falling-down-falling-down-cpanel-whm-authentication-bypass-cve-2026-41940/ (opens in a new tab)
• CVE authority reference: https://www.bleepingcomputer.com/news/security/critrical-cpanel-flaw-mass-exploited-in-sorry-ransomware-attacks/ (opens in a new tab)
• Exploit or technical research: https://github.com/watchtowrlabs/watchTowr-vs-cPanel-WHM-AuthBypass-to-RCE.py (opens in a new tab)
• CVE authority reference: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-41940 (opens in a new tab)

Test or Research Source

• Source: https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-41940.yaml (opens in a new tab)
• Tags: manual-review
• Research basis: Research note for exploit techniques associated with CVE-2026-41940

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/ (opens in a new tab) .