Medium (6.5). EPSS 1.0% chance of exploitation in the next 30 days. Fixed in io.netty:netty-codec-http 4.1.86.Final.
Netty project is an event-driven asynchronous network application framework. Starting in version 4.1.83.Final and prior to 4.1.86.Final, when calling `DefaultHttpHeadesr.set` with an _iterator_ of values, header value validation was not performed, allowing malicious header values in the iterator to perform HTTP Response Splitting. This issue has been patched in version 4.1.86.Final. Integrators can work around the issue by changing the `DefaultHttpHeaders.set(CharSequence, Iterator<?>)` call, into a `remove()` call, and call `add()` in a loop over the iterator of values.
Severity
CVSS 3.1
6.5 medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
EPSS
1.0% chance of exploitation in the next 30 days; higher than 61% of CVEs (scores of 2026-10-31)