Can you explain this vulnerability to me?

HestiaCP versions 1.2.0 through 1.9.4 contain an IP spoofing vulnerability where the software trusts the CF-Connecting-IP HTTP header without verifying that the request actually originated from Cloudflare's network.

This allows unauthenticated remote attackers to supply an arbitrary IP address in this header, effectively spoofing their IP address.

As a result, attackers can bypass authentication security controls, circumvent fail2ban brute-force protection, bypass per-user IP allowlists, and poison authentication audit logs by pretending to be trusted IP addresses.

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How can this vulnerability impact me? :

This vulnerability can have serious security impacts including allowing attackers to bypass authentication mechanisms without needing valid credentials.

Attackers can evade brute-force protection systems like fail2ban, making it easier to attempt password guessing attacks.

They can also bypass IP-based access controls such as per-user IP allowlists, gaining unauthorized access.

Additionally, attackers can poison authentication audit logs by spoofing trusted IP addresses, making it difficult to trace malicious activity.

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How can this vulnerability be detected on my network or system? Can you suggest some commands?

The vulnerability involves spoofing the CF-Connecting-IP HTTP header to bypass authentication and security controls. Detection can focus on monitoring HTTP requests for suspicious or unexpected CF-Connecting-IP header values that do not match the actual source IP address.

You can use network monitoring or web server logs to identify requests where the CF-Connecting-IP header is present and does not correspond to known Cloudflare IP ranges or the actual client IP.

• Use tools like tcpdump or Wireshark to capture HTTP traffic and filter for CF-Connecting-IP headers.
• Example tcpdump command to capture HTTP headers containing CF-Connecting-IP: tcpdump -A -s 0 'tcp port 80 or tcp port 443' | grep 'CF-Connecting-IP'
• Check web server access logs (e.g., Apache or Nginx) for requests with the CF-Connecting-IP header and verify if the IPs are from trusted Cloudflare ranges.
• Use fail2ban logs to detect if brute-force protections are being bypassed unusually, which may indicate exploitation.

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What immediate steps should I take to mitigate this vulnerability?

Immediate mitigation steps include disabling the web terminal and restricting access to the management port to prevent exploitation.

• Disable the web terminal using the command: v-delete-sys-web-terminal
• Restrict access to port 8083 (the HestiaCP management port) using firewall rules to limit connections only to trusted IP addresses.

Additionally, monitor for updates or patches from the HestiaCP project, as fixes have been merged but no official release was available as of May 19, 2026.

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How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:

The IP spoofing vulnerability in HestiaCP allows attackers to bypass authentication controls, circumvent brute-force protections, and poison authentication audit logs by spoofing trusted IP addresses. This undermines the integrity and reliability of security controls and audit trails.

Such weaknesses can negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require robust access controls, accurate logging, and protection against unauthorized access. The ability to spoof IP addresses and bypass security mechanisms could lead to unauthorized data access or manipulation, thereby violating these regulatory requirements.

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