Full Report
Improper certificate validation vulnerability (CVE-2026-15243) has been found in Apereo CAS Client software.
Analysis Summary
# Vulnerability: Improper Certificate Validation in Apereo CAS Client
## CVE Details
- **CVE ID:** CVE-2026-15243
- **CVSS Score:** Not explicitly provided in the source (Typically High for MITM-based credential interception)
- **CWE:** CWE-297 (Improper Validation of Certificate with Host Mismatch)
## Affected Systems
- **Products:** Java Apereo CAS Client / Jasig CAS Client
- **Versions:**
- Java Apereo CAS Client: 4.1.0 (Confirmed)
- Jasig CAS Client: 3.6.4 (Confirmed)
- *Note: Other versions may also be affected as vendor contact attempts were unsuccessful.*
- **Configurations:** Systems where the client is configured to use URLs matching specific allowlists or regular expressions.
## Vulnerability Description
The Apereo CAS Client fails to properly validate the hostname on certificates provided during the TLS handshake. While the software checks if a certificate is trusted by a Certificate Authority (CA), it accepts any CA-trusted certificate regardless of whether the hostname on the certificate matches the server's actual hostname. This occurs as long as the target URL matches a pre-configured allowlist or regex in the client settings.
## Exploitation
- **Status:** Reported via responsible disclosure; No mentions of active exploitation in the wild.
- **Complexity:** Medium (Requires the ability to intercept traffic).
- **Attack Vector:** Network (Specifically via Man-in-the-Middle positions such as DNS poisoning, rogue Wi-Fi, or malicious proxies).
## Impact
- **Confidentiality:** High (Intercepting CAS exchanges allows for the capture of Ticket-Granting Tickets (TGT) and Service Tickets).
- **Integrity:** High (Attackers can obtain Service Tickets to impersonate users on downstream services).
- **Availability:** Low/None.
## Remediation
### Patches
- **No official patches currently available:** The advisory indicates that attempts to contact the maintainers were unsuccessful.
### Workarounds
- **Network Security:** Ensure the path between the CAS Client and the CAS Server is secure and protected against MITM attacks.
- **Certificate Pinning:** If possible within the implementation, enforce strict certificate pinning or manual hostname verification overrides.
- **Egress Filtering:** Limit the ability of the client to reach untrusted networks where rogue proxies or DNS servers might reside.
## Detection
- **Indicators of Compromise:** Unusual source IPs for authenticated sessions; discrepancies between user login locations and Ticket-Granting Ticket usage.
- **Detection methods and tools:**
- Review application logs for unexpected hostnames being accepted in TLS connections.
- Periodic audits of the CAS client configuration, specifically regex/allowlist patterns.
## References
- **CVE Record:** hxxps[://]www[.]cve[.]org/CVERecord?id=CVE-2026-15243
- **CERT Polska Advisory:** hxxps[://]cert[.]pl/en/posts/2026/07/vulnerability-apereo-cas/ (Derived from report)
- **CWE-297 Definition:** hxxps[://]cwe[.]mitre[.]org/data/definitions/297[.]html