CVE-2022-41915 is a medium-severity vulnerability affecting the Netty project, an event-driven asynchronous network application framework widely used in Java-based network applications and services. The vulnerability exists in versions starting from 4.1.83.Final up to, but not including, 4.1.86.Final. The issue arises when the method DefaultHttpHeaders.set(CharSequence, Iterator<?>) is called with an iterator of header values. In this scenario, the header value validation is bypassed, allowing malicious input containing CRLF (Carriage Return Line Feed) sequences to be injected into HTTP headers. This improper neutralization of CRLF sequences (CWE-113) leads to HTTP Response Splitting attacks, where an attacker can manipulate HTTP responses by injecting additional headers or even crafting multiple responses. This can result in cache poisoning, cross-site scripting (XSS), and other web-based attacks. The root cause is an interpretation conflict (CWE-436) in how the iterator of header values is processed without proper validation. The vulnerability has been addressed in Netty version 4.1.86.Final by enforcing validation on header values when using the iterator-based set method. As a workaround, integrators can replace the vulnerable call with a remove() followed by multiple add() calls iterating over the header values, ensuring each value is individually validated. No known exploits have been reported in the wild to date, but the vulnerability poses a risk to applications relying on vulnerable Netty versions for HTTP header management.

For European organizations, this vulnerability can have significant implications, especially for those operating web services, APIs, or networked applications built on the Netty framework. HTTP Response Splitting can enable attackers to perform cache poisoning, leading to the delivery of malicious content to end users, potentially damaging brand reputation and violating data protection regulations such as GDPR. Additionally, it can facilitate cross-site scripting attacks, compromising user confidentiality and integrity of web sessions. The vulnerability affects the integrity and confidentiality of data processed by affected applications and can degrade availability if exploited to disrupt normal HTTP response behavior. Given Netty's widespread use in enterprise middleware, telecom infrastructure, and cloud services, organizations in sectors such as finance, healthcare, and critical infrastructure in Europe could face targeted exploitation attempts. The absence of known exploits reduces immediate risk, but the ease of exploitation through crafted HTTP headers and the broad deployment of Netty make proactive mitigation essential.

European organizations should prioritize upgrading all Netty dependencies to version 4.1.86.Final or later to ensure the vulnerability is patched. Where immediate upgrade is not feasible, developers should refactor code to avoid using DefaultHttpHeaders.set(CharSequence, Iterator<?>) and instead implement the recommended workaround: remove existing headers and add new ones individually with validation. Security teams should audit applications for usage of vulnerable Netty versions and review HTTP header handling logic. Implementing Web Application Firewalls (WAFs) with rules to detect and block CRLF injection attempts can provide an additional layer of defense. Monitoring HTTP traffic for anomalous header patterns indicative of response splitting attempts is advised. Finally, organizations should conduct security testing, including fuzzing and penetration testing focused on HTTP header injection vectors, to validate the effectiveness of mitigations.