phpCAS vulnerable to Service Hostname Discovery ExploitationGHSA-8q72-6qq8-xv64
HIGHFix: apereo/phpCAS@b759361GHSA-8q72-6qq8-xv64 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.
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-8q72-6qq8-xv64.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
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 |
Affected Products
phpcasapereofedorafedoraprojectDetection & 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 GHSA-8q72-6qq8-xv64 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.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is GHSA-8q72-6qq8-xv64 in your dependencies?
Find it across Packagist, including transitive dependencies.