CVE-2026-23795: Apache Syncope Console XXE Vulnerability

CVE-2026-23795 Overview

CVE-2026-23795 is an Improper Restriction of XML External Entity Reference (XXE) vulnerability affecting Apache Syncope Console. The vulnerability allows an administrator with adequate entitlements to create or edit Keymaster parameters via the Console to construct malicious XML text and launch an XXE attack. Successful exploitation results in sensitive data leakage from the affected system.

Critical Impact

Authenticated administrators can exploit XXE injection in Keymaster parameter handling to exfiltrate sensitive data from the server, including configuration files, credentials, and internal system information.

Affected Products

• Apache Syncope versions 3.0 through 3.0.15
• Apache Syncope versions 4.0 through 4.0.3

Discovery Timeline

• 2026-02-03 - CVE-2026-23795 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2026-23795

Vulnerability Analysis

This vulnerability is classified as CWE-611 (Improper Restriction of XML External Entity Reference). The flaw exists in the Apache Syncope Console's handling of XML input when administrators create or modify Keymaster parameters. The XML parser does not properly restrict external entity references, allowing an attacker to craft malicious XML payloads that reference external resources or local files.

When the vulnerable XML parser processes the malicious input, it resolves external entity references, which can be leveraged to read arbitrary files from the server's filesystem or make requests to internal network resources. This vulnerability requires administrative privileges to exploit, as only users with specific entitlements can access the Keymaster parameter functionality in the Console.

Root Cause

The root cause of this vulnerability is the improper configuration of the XML parser used in the Apache Syncope Console. The parser fails to disable external entity processing and DTD (Document Type Definition) processing, which are common attack vectors for XXE vulnerabilities. When XML input containing external entity declarations is processed, the parser attempts to resolve these references, leading to information disclosure.

Attack Vector

The attack requires network access to the Apache Syncope Console and valid administrative credentials with entitlements to manage Keymaster parameters. An attacker would craft a malicious XML payload containing external entity declarations pointing to sensitive files (such as /etc/passwd or application configuration files) or internal network resources. When this payload is submitted through the Console's Keymaster parameter interface, the vulnerable XML parser processes the external entities, returning the contents of the referenced resources in the response or error messages.

For example, an attacker could define an external entity that references a local file system path, and when the XML is parsed, the file contents would be substituted into the XML document, potentially exposing sensitive configuration data, credentials, or system information.

Detection Methods for CVE-2026-23795

Indicators of Compromise

• Unusual XML payloads containing <!DOCTYPE> or <!ENTITY> declarations in Keymaster parameter requests
• HTTP requests to the Console containing external entity references with file://, http://, or ftp:// protocols
• Error messages revealing local file paths or internal network responses
• Anomalous access patterns to Keymaster parameter management functionality

Detection Strategies

• Monitor Apache Syncope Console logs for XML parsing errors or unusual entity resolution attempts
• Implement Web Application Firewall (WAF) rules to detect and block XXE payload patterns in request bodies
• Review audit logs for administrative actions involving Keymaster parameter creation or modification
• Deploy intrusion detection signatures to identify common XXE attack patterns

Monitoring Recommendations

• Enable detailed logging for the Apache Syncope Console application
• Monitor for outbound connections from the Syncope server to unexpected internal or external destinations
• Set up alerts for failed file access attempts that may indicate probing for readable files
• Track changes to Keymaster parameters and correlate with user activity

How to Mitigate CVE-2026-23795

Immediate Actions Required

• Upgrade Apache Syncope to version 3.0.16 (for 3.x branch) or 4.0.4 (for 4.x branch) immediately
• Review administrative user accounts and restrict Keymaster parameter management entitlements to essential personnel only
• Audit Keymaster parameter logs for any suspicious modifications or unusual XML content
• Implement network segmentation to limit the impact of potential data exfiltration

Patch Information

Apache has released security patches that address this vulnerability. Users running Apache Syncope versions 3.0 through 3.0.15 should upgrade to version 3.0.16. Users running versions 4.0 through 4.0.3 should upgrade to version 4.0.4. These patched versions properly configure the XML parser to disable external entity processing. For additional details, refer to the Apache Mailing List Thread and the OpenWall OSS Security Email.

Workarounds

• Restrict access to the Apache Syncope Console administrative interface using network-level controls
• Remove or limit Keymaster parameter management entitlements from non-essential administrative accounts
• Implement input validation at the application gateway level to filter XML payloads containing external entity declarations
• Consider placing a reverse proxy with XXE filtering capabilities in front of the Syncope Console

# Example: Restricting access to Syncope Console via iptables
# Allow only specific trusted IP addresses to access the Console port
iptables -A INPUT -p tcp --dport 8080 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP