CVE-2022-31042 is a medium-severity vulnerability affecting the Guzzle PHP HTTP client, specifically versions prior to 6.5.7 and versions from 7.0.0 up to but not including 7.4.4. Guzzle is widely used in PHP applications to facilitate HTTP requests. The vulnerability pertains to improper handling of the 'Cookie' HTTP headers during redirects. When a request is made over HTTPS and the server responds with a redirect to an HTTP URL, or when a redirect points to a different host, sensitive 'Cookie' headers that may contain authentication tokens or session identifiers are forwarded improperly. This occurs because only cookies managed by Guzzle's cookie middleware were stripped during redirects, while any manually added 'Cookie' headers were not removed. Consequently, sensitive cookie data could be exposed to unauthorized actors if the redirect leads to a less secure or unintended destination. The fix implemented in Guzzle 7.4.4 and 6.5.7 ensures that all 'Cookie' headers are stripped on redirects, and only cookies deemed appropriate by the middleware are re-added. Users unable to upgrade are advised to disable redirects or implement custom redirect middleware to prevent this exposure. This vulnerability is classified under CWE-200, indicating exposure of sensitive information to unauthorized actors. No known exploits have been reported in the wild to date, but the risk remains significant due to the potential leakage of sensitive session data during redirects.

For European organizations, the exposure of sensitive cookie information during HTTP redirects can lead to session hijacking, unauthorized access, and data breaches. Many European enterprises rely on PHP-based web applications that use Guzzle for backend HTTP communications, including financial institutions, e-commerce platforms, healthcare providers, and government services. The inadvertent forwarding of cookies to untrusted or downgraded HTTP endpoints can allow attackers to intercept session tokens, leading to compromised user accounts and unauthorized data access. This risk is heightened in environments where HTTPS to HTTP redirects occur, either due to misconfigurations or legacy systems. The impact extends to confidentiality breaches, potential integrity violations if attackers manipulate sessions, and availability concerns if attackers disrupt authenticated sessions. Given the stringent data protection regulations in Europe, such as GDPR, organizations may also face legal and compliance repercussions if sensitive user data is exposed. The absence of known exploits suggests that proactive mitigation can effectively prevent exploitation, but the widespread use of Guzzle in PHP applications means the attack surface is considerable.

1. Immediate Upgrade: Organizations should prioritize upgrading all affected Guzzle versions to at least 6.5.7 or 7.4.4 to ensure the vulnerability is patched. 2. Disable Automatic Redirects: If upgrading is not immediately feasible, disable automatic HTTP redirects in Guzzle to prevent unintended cookie forwarding. 3. Implement Custom Redirect Middleware: Develop and deploy custom redirect handling logic that explicitly strips sensitive headers, including manually added 'Cookie' headers, before following redirects. 4. Audit and Sanitize Cookies: Review application code to avoid manually adding sensitive cookies to requests unless necessary, and ensure cookie management is centralized through Guzzle's middleware. 5. Monitor Redirects: Log and monitor HTTP redirect responses to detect any redirects from HTTPS to HTTP or cross-host redirects that could expose cookies. 6. Network Controls: Employ network-level controls such as HTTPS enforcement and redirect blocking to minimize exposure to insecure redirects. 7. Security Testing: Incorporate this vulnerability check into regular security assessments and penetration testing to verify that cookie leakage does not occur during redirects. 8. Educate Developers: Train development teams on secure HTTP client usage patterns, emphasizing the risks of manual cookie header manipulation and the importance of middleware use.