CVE-2026-25577 is a vulnerability in the Emmett web framework core component, specifically in versions prior to 1.3.11. The flaw stems from the improper handling of exceptions during the parsing of HTTP Cookie headers within the mmett_core.http.wrappers.Request class. When a malformed Cookie header is received, the framework fails to catch the resulting CookieError exception, causing an uncaught exception that leads to an HTTP 500 Internal Server Error response. This behavior can be exploited by unauthenticated attackers who send specially crafted HTTP requests with malformed Cookie headers, triggering a denial of service by crashing or destabilizing the web application. The vulnerability is classified under CWE-248 (Uncaught Exception) and CWE-307 (Improper Restriction of Excessive Authentication Attempts), highlighting the lack of proper error handling and potential for abuse without authentication. The CVSS v3.1 base score is 7.5, reflecting a high severity due to network attack vector, no required privileges or user interaction, and a significant impact on availability. The vulnerability does not affect confidentiality or integrity but can cause service outages. The issue is resolved in Emmett framework version 1.3.11, where proper exception handling for CookieError is implemented to prevent the server from crashing on malformed cookies. No public exploits have been reported yet, but the ease of exploitation and impact on availability make this a critical patching priority for affected users.

For European organizations, the primary impact of CVE-2026-25577 is denial of service, which can disrupt web applications built on the Emmett framework. This can lead to downtime, loss of service availability, and potential reputational damage, especially for service providers and e-commerce platforms relying on Emmett. Since exploitation requires no authentication and can be triggered remotely, attackers can cause widespread disruption with minimal effort. Critical sectors such as finance, healthcare, and government services that depend on web applications may experience operational interruptions. Additionally, denial of service can be leveraged as part of multi-stage attacks or to distract security teams. The lack of confidentiality or integrity impact limits data breach risks, but service unavailability alone can have significant business and regulatory consequences under European data protection and service continuity regulations.

European organizations should immediately upgrade all Emmett framework instances to version 1.3.11 or later to ensure the vulnerability is patched. In environments where immediate patching is not feasible, implementing web application firewalls (WAFs) to detect and block malformed Cookie headers can provide temporary protection. Monitoring HTTP 500 error rates and unusual traffic patterns related to cookie parsing can help detect exploitation attempts. Developers should review error handling practices in their applications to ensure robustness against malformed inputs. Network-level rate limiting and IP reputation filtering can reduce the risk of automated exploitation attempts. Additionally, organizations should maintain an inventory of applications using the Emmett framework to prioritize patching and incident response. Regular security assessments and penetration testing focusing on input validation and exception handling are recommended to identify similar weaknesses.