CVE-2026-27127

Craft is a content management system (CMS). In versions 4.5.0-RC1 through 4.16.18 and 5.0.0-RC1 through 5.8.22, the SSRF validation in Craft CMS’s GraphQL Asset mutation performs DNS resolution separately from the HTTP request. This Time-of-Check-Time-of-Use (TOCTOU) vulnerability enables DNS rebinding attacks, where an attacker’s DNS server returns different IP addresses for validation compared to the actual request. This is a bypass of the security fix for CVE-2025-68437 that allows access to all blocked IPs, not just IPv6 endpoints. Exploitation requires GraphQL schema permissions for editing assets in the <VolumeName> volume and creating assets in the <VolumeName> volume. These permissions may be granted to authenticated users with appropriate GraphQL schema access and/or Public Schema (if misconfigured with write permissions). Versions 4.16.19 and 5.8.23 patch the issue.

Craft is a content management system (CMS). In versions 4.5.0-RC1 through 4.16.18 and 5.0.0-RC1 through 5.8.22, the SSRF validation in Craft CMS’s GraphQL Asset mutation performs DNS resolution separately from the HTTP request. This Time-of-Check-Time-of-Use (TOCTOU) vulnerability enables DNS rebinding attacks, where an attacker’s DNS server returns different IP addresses for validation compared to the actual request. This is a bypass of the security fix for CVE-2025-68437 that allows access to all blocked IPs, not just IPv6 endpoints. Exploitation requires GraphQL schema permissions for editing assets in the <VolumeName> volume and creating assets in the <VolumeName> volume. These permissions may be granted to authenticated users with appropriate GraphQL schema access and/or Public Schema (if misconfigured with write permissions). Versions 4.16.19 and 5.8.23 patch the issue.

Summary

The SSRF validation in Craft CMS’s GraphQL Asset mutation performs DNS resolution separately from the HTTP request. This Time-of-Check-Time-of-Use (TOCTOU) vulnerability enables DNS rebinding attacks, where an attacker’s DNS server returns different IP addresses for validation compared to the actual request.

This is a bypass of the security fix for CVE-2025-68437 (GHSA-x27p-wfqw-hfcc) that allows access to all blocked IPs, not just IPv6 endpoints.

Severity

Bypass of cloud metadata SSRF protection for all blocked IPs

Required Permissions

Exploitation requires GraphQL schema permissions for:

• Edit assets in the <VolumeName> volume
• Create assets in the <VolumeName> volume

These permissions may be granted to:

• Authenticated users with appropriate GraphQL schema access
• Public Schema (if misconfigured with write permissions)

Technical Details

Vulnerable Code Flow

The code at src/gql/resolvers/mutations/Asset.php performs two separate DNS lookups:

// VALIDATION PHASE: First DNS resolution at time T1
private function validateHostname(string $url): bool
{
    $hostname = parse_url($url, PHP_URL_HOST);
    $ip = gethostbyname($hostname);  // DNS Lookup #1 - Returns safe IP

    if (in_array($ip, [
        '169.254.169.254',   // AWS, GCP, Azure IMDS
        '169.254.170.2',     // AWS ECS metadata
        '100.100.100.200',   // Alibaba Cloud
        '192.0.0.192',       // Oracle Cloud
    ])) {
        return false;  // Check passes - IP looks safe
    }
    return true;
}

// ... time gap between validation and request ...

// REQUEST PHASE: Second DNS resolution at time T2 (inside Guzzle)
$response = $client->get($url);  // DNS Lookup #2 - Guzzle resolves DNS AGAIN
                                  // Now returns 169.254.169.254!

Root Cause

Two separate DNS lookups occur:

1. Validation: gethostbyname() in validateHostname()
2. Request: Guzzle's internal DNS resolution via libcurl

An attacker controlling a DNS server can return different IPs for each query.

Bypass Mechanism

+-----------------------------------------------------------------------------+
| Attacker's DNS Server: evil.attacker.com                                    |
+-----------------------------------------------------------------------------+
| Query 1 (Validation - T1):                                                  |
|   Request:  A record for evil.attacker.com                                  |
|   Response: 1.2.3.4 (safe IP, TTL: 0)                                       |
|   Result:   Validation PASSES                                               |
+-----------------------------------------------------------------------------+
| Query 2 (Guzzle Request - T2):                                              |
|   Request:  A record for evil.attacker.com                                  |
|   Response: 169.254.169.254 (metadata IP, TTL: 0)                           |
|   Result:   Request goes to blocked IP -> CREDENTIALS STOLEN                |
+-----------------------------------------------------------------------------+

Target Endpoints via DNS Rebinding

DNS rebinding allows access to all blocked IPs:

| Target | Rebind To | Impact | |--------|-----------|--------| | AWS IMDS | 169.254.169.254 | IAM credentials, instance identity | | AWS ECS | 169.254.170.2 | Container credentials | | GCP Metadata | 169.254.169.254 | Service account tokens | | Azure Metadata | 169.254.169.254 | Managed identity tokens | | Alibaba Cloud | 100.100.100.200 | Instance credentials | | Oracle Cloud | 192.0.0.192 | Instance metadata | | Internal Services | 127.0.0.1, 10.x.x.x | Internal APIs, databases |

Attack Scenario

1. Attacker sets up DNS server with alternating responses
2. Attacker sends mutation with `url:…

Craft is a content management system (CMS). In versions 4.5.0-RC1 through 4.16.18 and 5.0.0-RC1 through 5.8.22, the SSRF validation in Craft CMS’s GraphQL Asset mutation performs DNS resolution separately from the HTTP request. This Time-of-Check-Time-of-Use (TOCTOU) vulnerability enables DNS rebinding attacks, where an attacker’s DNS server returns different IP addresses for validation compared to the actual request. This is a bypass of the security fix for CVE-2025-68437 that allows access to all blocked IPs, not just IPv6 endpoints. Exploitation requires GraphQL schema permissions for editing assets in the <VolumeName> volume and creating assets in the <VolumeName> volume. These permissions may be granted to authenticated users with appropriate GraphQL schema access and/or Public Schema (if misconfigured with write permissions). Versions 4.16.19 and 5.8.23 patch the issue.

Craft is a content management system (CMS). In versions 4.5.0-RC1 through 4.16.18 and 5.0.0-RC1 through 5.8.22, the SSRF validation in Craft CMS’s GraphQL Asset mutation performs DNS resolution separately from the HTTP request. This Time-of-Check-Time-of-Use (TOCTOU) vulnerability enables DNS rebinding attacks, where an attacker’s DNS server returns different IP addresses for validation compared to the actual request. This is a bypass of the security fix for CVE-2025-68437 that allows access to all blocked IPs, not just IPv6 endpoints. Exploitation requires GraphQL schema permissions for editing assets in the <VolumeName> volume and creating assets in the <VolumeName> volume. These permissions may be granted to authenticated users with appropriate GraphQL schema access and/or Public Schema (if misconfigured with write permissions). Versions 4.16.19 and 5.8.23 patch the issue.

Summary

The SSRF validation in Craft CMS’s GraphQL Asset mutation performs DNS resolution separately from the HTTP request. This Time-of-Check-Time-of-Use (TOCTOU) vulnerability enables DNS rebinding attacks, where an attacker’s DNS server returns different IP addresses for validation compared to the actual request.

This is a bypass of the security fix for CVE-2025-68437 (GHSA-x27p-wfqw-hfcc) that allows access to all blocked IPs, not just IPv6 endpoints.

Severity

Bypass of cloud metadata SSRF protection for all blocked IPs

Required Permissions

Exploitation requires GraphQL schema permissions for:

• Edit assets in the <VolumeName> volume
• Create assets in the <VolumeName> volume

These permissions may be granted to:

• Authenticated users with appropriate GraphQL schema access
• Public Schema (if misconfigured with write permissions)

Technical Details

Vulnerable Code Flow

The code at src/gql/resolvers/mutations/Asset.php performs two separate DNS lookups:

// VALIDATION PHASE: First DNS resolution at time T1
private function validateHostname(string $url): bool
{
    $hostname = parse_url($url, PHP_URL_HOST);
    $ip = gethostbyname($hostname);  // DNS Lookup #1 - Returns safe IP

    if (in_array($ip, [
        '169.254.169.254',   // AWS, GCP, Azure IMDS
        '169.254.170.2',     // AWS ECS metadata
        '100.100.100.200',   // Alibaba Cloud
        '192.0.0.192',       // Oracle Cloud
    ])) {
        return false;  // Check passes - IP looks safe
    }
    return true;
}

// ... time gap between validation and request ...

// REQUEST PHASE: Second DNS resolution at time T2 (inside Guzzle)
$response = $client->get($url);  // DNS Lookup #2 - Guzzle resolves DNS AGAIN
                                  // Now returns 169.254.169.254!

Root Cause

Two separate DNS lookups occur:

1. Validation: gethostbyname() in validateHostname()
2. Request: Guzzle's internal DNS resolution via libcurl

An attacker controlling a DNS server can return different IPs for each query.

Bypass Mechanism

+-----------------------------------------------------------------------------+
| Attacker's DNS Server: evil.attacker.com                                    |
+-----------------------------------------------------------------------------+
| Query 1 (Validation - T1):                                                  |
|   Request:  A record for evil.attacker.com                                  |
|   Response: 1.2.3.4 (safe IP, TTL: 0)                                       |
|   Result:   Validation PASSES                                               |
+-----------------------------------------------------------------------------+
| Query 2 (Guzzle Request - T2):                                              |
|   Request:  A record for evil.attacker.com                                  |
|   Response: 169.254.169.254 (metadata IP, TTL: 0)                           |
|   Result:   Request goes to blocked IP -> CREDENTIALS STOLEN                |
+-----------------------------------------------------------------------------+

Target Endpoints via DNS Rebinding

DNS rebinding allows access to all blocked IPs:

| Target | Rebind To | Impact | |--------|-----------|--------| | AWS IMDS | 169.254.169.254 | IAM credentials, instance identity | | AWS ECS | 169.254.170.2 | Container credentials | | GCP Metadata | 169.254.169.254 | Service account tokens | | Azure Metadata | 169.254.169.254 | Managed identity tokens | | Alibaba Cloud | 100.100.100.200 | Instance credentials | | Oracle Cloud | 192.0.0.192 | Instance metadata | | Internal Services | 127.0.0.1, 10.x.x.x | Internal APIs, databases |

Attack Scenario

1. Attacker sets up DNS server with alternating responses
2. Attacker sends mutation with `url:…

TuxCare rebuilt craftcms/cms to address 3 CVEs. Fixed in 3.9.15-p3+tuxcare.