CVE-2025-53641: Postiz SSRF Vulnerability

CVE-2025-53641 Overview

CVE-2025-53641 is a Server-Side Request Forgery (SSRF) vulnerability affecting Postiz, an AI-powered social media scheduling tool. The vulnerability exists in the Postiz frontend application, which allows an attacker to inject arbitrary HTTP headers into the middleware pipeline. This flaw enables a server-side request forgery condition that can be exploited to initiate unauthorized outbound requests from the server hosting the Postiz application.

Critical Impact

Attackers can leverage this SSRF vulnerability to make unauthorized outbound requests from the server, potentially accessing internal services, cloud metadata endpoints, or other sensitive resources that should not be externally accessible.

Affected Products

• Postiz versions 1.45.1 through 1.62.3
• Postiz frontend application middleware component

Discovery Timeline

• 2025-07-11 - CVE-2025-53641 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-53641

Vulnerability Analysis

This vulnerability stems from improper handling of HTTP headers in the Postiz frontend middleware. The application fails to properly sanitize or validate headers passed through the NextResponse.next() function, allowing attackers to inject arbitrary HTTP headers that are then processed by the middleware pipeline. This creates an SSRF condition where the server can be manipulated to make requests to unintended destinations.

The vulnerability is classified under CWE-918 (Server-Side Request Forgery), which occurs when a web application fetches a remote resource without sufficiently validating the user-supplied URL or request parameters. In this case, the injection occurs at the HTTP header level rather than directly through URL manipulation.

Root Cause

The root cause lies in the middleware implementation within apps/frontend/src/middleware.ts. The vulnerable code passed HTTP headers directly to NextResponse.next() without proper isolation, allowing user-controlled header values to influence server-side request behavior. The headers were being passed at the response level rather than being scoped to the request object.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can craft malicious HTTP requests with injected headers targeting the Postiz frontend application. These injected headers are then processed by the middleware, potentially causing the server to:

• Make requests to internal services or APIs
• Access cloud provider metadata endpoints (e.g., AWS IMDSv1, GCP metadata)
• Bypass network access controls and firewalls
• Exfiltrate sensitive data through controlled endpoints

// Vulnerable code (before patch)
return NextResponse.next({
  headers,
});

// Fixed code (after patch)
return NextResponse.next({
  request: {
    headers: headers,
  },
});

Source: GitHub Commit Details

Detection Methods for CVE-2025-53641

Indicators of Compromise

• Unusual outbound HTTP requests originating from the Postiz application server to internal IP ranges or cloud metadata endpoints
• Unexpected headers appearing in server logs or network traffic analysis
• Requests to localhost or internal service endpoints from the Postiz middleware
• Evidence of access to cloud metadata services (e.g., 169.254.169.254)

Detection Strategies

• Monitor network traffic for outbound requests to internal IP ranges (10.x.x.x, 172.16.x.x-172.31.x.x, 192.168.x.x) and loopback addresses
• Implement web application firewall (WAF) rules to detect and block SSRF patterns in HTTP headers
• Review Postiz application logs for anomalous middleware behavior or unexpected request patterns
• Deploy egress filtering to alert on connections to sensitive internal endpoints

Monitoring Recommendations

• Enable detailed logging for the Postiz frontend middleware to capture all incoming request headers
• Configure network monitoring to alert on traffic to cloud metadata endpoints from application servers
• Implement application-level monitoring to detect unusual request patterns in the Next.js middleware pipeline
• Review DNS logs for resolution of internal hostnames from the Postiz application server

How to Mitigate CVE-2025-53641

Immediate Actions Required

• Upgrade Postiz to version 1.62.3 or later immediately
• Audit application logs for evidence of exploitation attempts
• Review network logs for unauthorized outbound requests from Postiz servers
• Implement network segmentation to limit server access to internal resources

Patch Information

The vulnerability has been fixed in Postiz version 1.62.3. The patch modifies how headers are passed to NextResponse.next() by properly scoping them within a request object rather than passing them directly at the response level. This prevents header injection from affecting the middleware pipeline's request handling.

For detailed patch information, refer to the GitHub Security Advisory and the security commit.

Workarounds

• If immediate patching is not possible, consider placing a reverse proxy or WAF in front of the Postiz application to filter malicious headers
• Implement strict egress filtering to prevent the Postiz server from making outbound connections to internal services or metadata endpoints
• Restrict network access from the Postiz application server to only required external services
• Consider temporarily disabling the affected middleware routes until the patch can be applied

# Example: Block outbound requests to cloud metadata endpoints using iptables
iptables -A OUTPUT -d 169.254.169.254 -j DROP
iptables -A OUTPUT -d 169.254.0.0/16 -j DROP

# Example: Restrict outbound traffic to internal IP ranges
iptables -A OUTPUT -d 10.0.0.0/8 -j DROP
iptables -A OUTPUT -d 172.16.0.0/12 -j DROP
iptables -A OUTPUT -d 192.168.0.0/16 -j DROP