Introduction to CVE-2026-27129

Cybersecurity is critical in today’s digital landscape, particularly for system administrators and hosting providers. Recently, a serious vulnerability, CVE-2026-27129, was identified affecting Craft CMS. This flaw allows an attacker to bypass server-side request forgery (SSRF) protections, exposing Linux servers to various threats.

Summary of the Incident

This vulnerability affects Craft CMS versions 4.5.0-RC1 through 4.16.18 and 5.0.0-RC1 through 5.8.22. The issue arises from the misuse of the `gethostbyname()` function, which resolves only IPv4 addresses. When a hostname has only IPv6 (AAAA) records, the function does not correctly validate the input, leading to SSRF protection bypass.

Why This Matters

For system admins and hosting providers, this CVE is a significant concern. Successfully exploiting this vulnerability allows attackers to manipulate requests, potentially extracting sensitive data. If your web application firewall fails to mitigate brute-force attacks or similar threats, your server security is severely compromised.

Mitigation Steps to Enhance Server Security

Deploying effective mitigation strategies is crucial. Here are essential steps to safeguard your Linux servers:

• Update to the latest versions of Craft CMS (4.16.19 or above, 5.8.23 or above).
• Review and tighten GraphQL schema permissions to minimize asset editing access.
• Implement stringent controls on write access for asset volumes.
• Utilize a comprehensive web application firewall for enhanced malware detection.

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