CVE-2022-39369 is a high-severity (CVSS 8) CWE-99 vulnerability in apereo/phpcas. A fix is available for apereo/phpcas — see the affected versions and patch details below.
Service Hostname Discovery Exploitation in phpCAS
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2022-39369 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
apereo/phpcasReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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.
Patch
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.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | apereo/phpcas | all versions | 1.6.0composer require apereo/phpcas:^1.6.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for apereo/phpcas, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update apereo/phpcas to 1.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2022-39369 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2022-39369 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2022-39369. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2022-39369 in your dependencies?
O3 Security finds CVE-2022-39369 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.