CVE-2026-24472 is a vulnerability in the honojs hono web application framework's Cache Middleware prior to version 4.11.7. The root cause is the middleware's failure to properly respect standard HTTP cache control directives, specifically 'Cache-Control: private' and 'Cache-Control: no-store'. These headers are designed to prevent sensitive or user-specific responses from being cached by shared caches or proxies. Due to this improper handling, responses containing private or authenticated information may be cached inadvertently. This cached data can then be served to unauthorized users, leading to information disclosure. The vulnerability does not affect the integrity or availability of the system but compromises confidentiality. Exploitation requires no authentication or user interaction and can be performed remotely, increasing the risk. The CVSS v3.1 base score is 5.3 (medium severity), reflecting the moderate impact and ease of exploitation. The issue was addressed in hono version 4.11.7 by correcting the cache middleware to honor cache control headers properly. No known exploits have been reported in the wild as of the publication date. The vulnerability is classified under CWE-524 (Information Exposure Through Cache) and CWE-613 (Insufficient Session Expiration).

For European organizations, this vulnerability poses a risk of unauthorized disclosure of sensitive or authenticated data through improperly cached HTTP responses. This could include personal data protected under GDPR, internal business information, or session-specific content. Exposure of such data may lead to privacy violations, regulatory penalties, reputational damage, and potential exploitation by attackers for further attacks such as session hijacking or social engineering. Since the vulnerability can be exploited remotely without authentication, it increases the attack surface for web applications using the affected hono versions. Organizations relying on honojs hono for critical web services or handling sensitive user data are particularly at risk. The impact is primarily on confidentiality, with no direct effect on system integrity or availability. Prompt patching is essential to mitigate these risks and maintain compliance with European data protection regulations.

European organizations should immediately upgrade all instances of honojs hono to version 4.11.7 or later, where the cache middleware properly respects HTTP cache control headers. In addition, conduct a thorough review of web application caching policies to ensure sensitive responses are correctly marked with appropriate cache control headers such as 'Cache-Control: private', 'Cache-Control: no-store', and 'Pragma: no-cache'. Implement strict cache validation and expiration strategies on both server and proxy layers. Monitor web server and application logs for unusual cache-related behavior or unauthorized access patterns. Where feasible, employ web application firewalls (WAFs) configured to detect and block anomalous caching behavior. Educate development teams on secure cache management best practices to prevent recurrence. Finally, perform regular security assessments and penetration testing focused on caching mechanisms to identify and remediate similar issues proactively.