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CVE-2026-56020 Webmin CVE debrief

CVE-2026-56020 is a critical vulnerability in the Webmin HTTP server (miniserv.pl) that allows unauthenticated attackers to impersonate any user with a configured SSL client certificate by sending a forged HTTP header. This vulnerability enables remote attackers to spoof certificate DNs and authenticate as any user. The issue was fixed in version 2.641 of Webmin. Organizations using Webmin should prioritize patching to prevent potential authentication bypass attacks.

Vendor
Webmin
Product
Unknown
CVSS
CRITICAL 9.2
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-18
Original CVE updated
2026-06-22
Advisory published
2026-06-18
Advisory updated
2026-06-22

Who should care

System administrators and security teams responsible for Webmin installations should be aware of this vulnerability. Given the critical severity (CVSS score of 9.2), immediate attention is required to prevent potential exploitation.

Technical summary

The Webmin HTTP server (miniserv.pl) is vulnerable to an authentication bypass attack. Unauthenticated attackers can impersonate any user with a configured SSL client certificate by sending a forged HTTP header. This allows remote attackers to spoof certificate DNs and authenticate as any user. The vulnerability is characterized by the following CVSS vector: CVSS:4.0/AV:N/AC:L/AT:P/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. The weakness associated with this vulnerability is CWE-290.

Defensive priority

high

Recommended defensive actions

  • Immediately upgrade Webmin to version 2.641 or later.
  • Review and update SSL client certificate configurations to ensure only authorized users have access.
  • Implement additional monitoring to detect potential authentication bypass attempts.
  • Restrict access to the Webmin HTTP server to trusted IP addresses or networks.
  • Consider implementing a Web Application Firewall (WAF) to detect and prevent exploitation attempts.
  • Regularly review Webmin security advisories and updates to stay informed about potential vulnerabilities.

Evidence notes

The information provided is based on data from the National Vulnerability Database (NVD) and other reliable sources. The CVE record and NVD detail pages provide comprehensive information about the vulnerability, including its CVSS score, vector, and references.

Official resources

public