CVE-2026-2556: cskefu SSRF Vulnerability

CVE-2026-2556 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in cskefu up to version 8.0.1. This issue affects the file com/cskefu/cc/controller/resource/MediaController.java within the Endpoint component. The manipulation of the url argument enables attackers to forge server-side requests, potentially allowing access to internal resources, sensitive data exfiltration, or pivoting to other internal systems. The attack can be initiated remotely by authenticated users. The exploit has been publicly disclosed, and the vendor was contacted early about this disclosure but did not respond.

Critical Impact

Attackers can leverage this SSRF vulnerability to make arbitrary HTTP requests from the server, potentially accessing internal services, cloud metadata endpoints, or sensitive internal resources that are otherwise not accessible from external networks.

Affected Products

• cskefu up to version 8.0.1
• com/cskefu/cc/controller/resource/MediaController.java component

Discovery Timeline

• 2026-02-16 - CVE-2026-2556 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-2556

Vulnerability Analysis

This vulnerability is classified as CWE-918: Server-Side Request Forgery (SSRF). The vulnerable endpoint in MediaController.java accepts a user-controlled url parameter without proper validation or sanitization. When the server processes this parameter, it makes outbound HTTP requests to the attacker-specified URL, effectively acting as a proxy for malicious requests.

SSRF vulnerabilities are particularly dangerous in cloud environments where internal metadata services (such as AWS 169.254.169.254 or similar) may be accessible. An attacker with low privileges can exploit this flaw to probe internal network infrastructure, access internal APIs, or retrieve sensitive configuration data that should not be externally accessible.

The attack requires network access and low-level authentication (authenticated user), but does not require any user interaction. The vulnerability affects confidentiality, integrity, and availability at a limited level, allowing attackers to read sensitive internal data, potentially modify requests to internal services, or cause service disruption.

Root Cause

The root cause of this vulnerability lies in the improper validation of the url parameter in the MediaController.java endpoint. The application accepts user-supplied URLs and initiates server-side HTTP requests without implementing adequate input validation, URL scheme restrictions, or allowlist-based filtering. This allows attackers to craft malicious URLs that target internal resources, localhost services, or cloud provider metadata endpoints.

Attack Vector

The attack vector is network-based, requiring the attacker to have authenticated access to the cskefu application. The attacker manipulates the url parameter in requests to the vulnerable MediaController endpoint. By supplying a crafted URL pointing to internal services or sensitive endpoints, the attacker can force the server to make requests on their behalf.

Typical attack scenarios include:

• Accessing cloud instance metadata services to retrieve credentials
• Probing internal network services and ports
• Bypassing firewall rules by using the server as a proxy
• Retrieving sensitive files from internal file servers

The vulnerability has been publicly disclosed, and technical details are available through the VulDB entry and the associated Feishu Document.

Detection Methods for CVE-2026-2556

Indicators of Compromise

• Unusual outbound HTTP requests from the cskefu application server to internal IP ranges (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
• Requests to cloud metadata endpoints such as 169.254.169.254 originating from the application server
• Access logs showing repeated requests to the MediaController endpoint with varying url parameter values containing internal hostnames or IPs
• Network traffic from the application server to unexpected internal services or ports

Detection Strategies

• Monitor application logs for requests to the MediaController endpoint with suspicious url parameter values targeting internal resources
• Implement network-level detection rules to alert on outbound connections from the application server to internal-only services
• Review web application firewall (WAF) logs for SSRF attack patterns in URL parameters
• Deploy endpoint detection to identify abnormal HTTP client behavior from the Java application process

Monitoring Recommendations

• Enable detailed logging for the MediaController endpoint to capture all url parameter values
• Configure network monitoring to track outbound connections from the cskefu application server
• Set up alerts for access attempts to cloud metadata services or internal network ranges
• Regularly audit access patterns to identify anomalous activity indicative of SSRF exploitation

How to Mitigate CVE-2026-2556

Immediate Actions Required

• Restrict network access to the vulnerable MediaController endpoint until a patch is available
• Implement input validation to allowlist only permitted URL schemes (e.g., https://) and domains
• Block outbound connections from the application server to internal network ranges and cloud metadata endpoints at the firewall level
• Review access logs for evidence of exploitation and investigate any suspicious activity

Patch Information

At the time of publication, the vendor (cskefu) has not responded to disclosure attempts and no official patch is available. Organizations should implement the workarounds listed below and monitor for vendor updates. For the latest information, refer to the VulDB entry.

Workarounds

• Deploy a web application firewall (WAF) rule to block requests to the MediaController endpoint containing suspicious URL patterns
• Implement network segmentation to prevent the application server from accessing sensitive internal services
• Configure egress filtering to block requests to internal IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.169.254)
• Consider disabling the affected MediaController functionality if not critical to operations
• Apply URL validation at the application level using an allowlist approach for permitted destination domains

Due to the lack of an official patch, these mitigations serve as temporary protective measures. Application-level fixes should implement proper URL validation including scheme restrictions, domain allowlisting, and blocking of internal IP ranges before processing the url parameter.