Summary
phpCAS vulnerable to Service Hostname Discovery Exploitation
Full technical description
Workarounds
This vulnerability only impacts the CAS client that the phpCAS library protects against. The problematic service URL discovery behavior in phpCAS < 1.6.0 will only be disabled, and thus you are not impacted from it, if the phpCAS configuration has the following setup:
phpCAS::setUrl()is called (a reminder that you have to pass in the full URL of the current page, rather than your service base URL), andphpCAS::setCallbackURL()is called, only when the proxy mode is enabled.- Alternatively, if your PHP's HTTP header input
X-Forwarded-Host,X-Forwarded-Server,Host,X-Forwarded-Proto,X-Forwarded-Protocolis sanitized before reaching PHP (by a reverse proxy, for example), you will not be impacted by this vulnerability.
Otherwise, you should upgrade the library to get the safe service discovery behavior.
If your CAS server service registry is configured to only allow known and trusted service URLs, the severity of the vulnerability is reduced substantially since an attacker must be in control of another authorized service.
Acknowledgement
We would like to thank Filip Hejsek for discovering this vulnerability, responsibly reporting it to the developers, and helping harden the patch.
Henry Pan and Joachim Fritschi helped with the patch and release effort as phpCAS developers.
Impact
The phpCAS library uses HTTP headers to determine the service URL used to validate tickets. This allows an attacker to control the host header and use a valid ticket granted for any authorized service in the same SSO realm (CAS server) to authenticate to the service protected by phpCAS.
Depending on the settings of the CAS server service registry in worst case this may be any other service URL (if the allowed URLs are configured to "^(https)://.*") or may be strictly limited to known and authorized services in the same SSO federation if proper URL service validation is applied.
This vulnerability may allow an attacker to gain access to a victim's account on a vulnerable CASified service without victim's knowledge, when the victim visits attacker's website while being logged in to the same CAS server.
CVE-2022-39369 has a CVSS score of 8.0 (High). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.6.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
phpCAS 1.6.0 is a major version upgrade that starts enforcing service URL discovery validation, because there is unfortunately no 100% safe default config to use in PHP. Starting this version, it is required to pass in an additional service base URL argument when constructing the client class.
For more information, please refer to the upgrading doc.
Frequently Asked Questions
- What is CVE-2022-39369? CVE-2022-39369 is a high-severity security vulnerability in apereo/phpcas (composer), affecting versions < 1.6.0. It is fixed in 1.6.0.
- How severe is CVE-2022-39369? CVE-2022-39369 has a CVSS score of 8.0 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of apereo/phpcas are affected by CVE-2022-39369? apereo/phpcas (composer) versions < 1.6.0 is affected.
- Is there a fix for CVE-2022-39369? Yes. CVE-2022-39369 is fixed in 1.6.0. Upgrade to this version or later.
- Is CVE-2022-39369 exploitable, and should I be worried? Whether CVE-2022-39369 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2022-39369 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2022-39369? Upgrade
apereo/phpcasto 1.6.0 or later.