CVE-2022-23500 is a medium-severity vulnerability affecting TYPO3, an open-source PHP-based web content management system widely used for building and managing websites. The vulnerability arises from uncontrolled recursion in the error handling mechanism of TYPO3 versions prior to 9.5.38, 10.4.33, 11.5.20, and 12.1.1. Specifically, when a user requests an invalid or non-existent resource via HTTP, TYPO3 triggers its page error handler. This handler attempts to retrieve content to display as an error message from another page. However, if this referenced page is also invalid or leads back to the error handler, the application enters a recursive loop, repeatedly calling itself. This uncontrolled recursion can amplify the initial request's impact, potentially exhausting server resources such as CPU and memory, leading to denial of service (DoS) conditions by exceeding web server limits. The vulnerability is related to CWE-674 (Uncontrolled Recursion), indicating a failure to properly limit recursive calls in the application logic. Although similar to CVE-2021-21359, this issue is distinct in its specific recursion trigger and affected TYPO3 versions. No known exploits have been reported in the wild, and patches have been released in the specified TYPO3 versions to address this issue. The vulnerability does not require authentication or user interaction beyond sending crafted HTTP requests to invalid resources, making it relatively easy to trigger if the system is exposed to untrusted users or the internet.

For European organizations using TYPO3, this vulnerability poses a risk primarily of denial of service. An attacker can exploit the uncontrolled recursion to overload web servers hosting TYPO3 sites, causing service outages or degraded performance. This can disrupt business operations, especially for organizations relying on TYPO3 for public-facing websites, intranets, or customer portals. The impact on confidentiality and integrity is minimal, as the vulnerability does not allow data leakage or unauthorized modification directly. However, the availability impact can be significant, particularly for high-traffic or critical websites. Organizations in sectors such as government, education, media, and e-commerce that use TYPO3 extensively may face reputational damage and operational disruption if targeted. Additionally, the recursive calls could increase server load, potentially leading to increased hosting costs or triggering automated mitigation measures that block legitimate traffic. Since no authentication is required, the attack surface includes any external user able to send HTTP requests, increasing the risk of opportunistic or automated attacks.

To mitigate this vulnerability, European organizations should immediately upgrade TYPO3 installations to the patched versions: 9.5.38 ELTS, 10.4.33, 11.5.20, or 12.1.1, depending on their current version. If immediate upgrading is not feasible, organizations can implement web server-level protections such as limiting the maximum number of recursive or nested requests via request filtering or rate limiting. Configuring web application firewalls (WAFs) to detect and block repeated requests to invalid or non-existent resources can help prevent triggering the recursion. Monitoring server logs for unusual spikes in 404 errors or recursive error page requests can provide early warning signs of exploitation attempts. Additionally, organizations should review and harden error handling configurations within TYPO3 to avoid referencing other pages in error messages or to implement safeguards that detect and break recursion loops. Network segmentation and restricting access to TYPO3 management interfaces can reduce exposure. Finally, maintaining regular backups and incident response plans will help mitigate the impact of any denial of service incidents.