CVE-2026-42577

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Netty ausnutzen, um Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren, vertrauliche Informationen offenzulegen oder einen Denial-of-Service-Zustand zu verursachen.

Ein Angreifer kann mehrere Schwachstellen in IBM Concert ausnutzen, um beliebigen Programmcode auszuführen, um einen Denial of Service Angriff durchzuführen, um Informationen offenzulegen, um Dateien zu manipulieren, um einen Cross-Site Scripting Angriff durchzuführen, um einen SQL-Injection Angriff durchzuführen und um Sicherheitsvorkehrungen zu umgehen.

## Summary Netty's epoll transport fails to detect and close TCP connections that receive a RST after being half-closed, leading to stale channels that are never cleaned up and, in some code paths, a 100% CPU busy-loop in the event loop thread. ## Affected versions All versions of 4.2.x `netty-transport-classes-epoll` up to and including 4.2.12.Final ## Fixed in 4.2.13.Final (fix merged into the `4.2` branch via [#16689](https://github.com/netty/netty/pull/16689); release not yet cut as of 2026-04-25). ## Severity **Medium** — Denial of Service (resource exhaustion / CPU spin) **CVSS:** 3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - **7.5** **CWE:** CWE-772: Missing Release of Resource after Effective Lifetime ## Description When a TCP connection using Netty's epoll transport has `ALLOW_HALF_CLOSURE` enabled (or is in a half-closed state via the HTTP codec), and the remote peer: 1. Sends a FIN (half-close), causing the server to mark the input as shutdown, then 2. Sends a RST (e.g. by closing with `SO_LINGER=0`) the server-side channel is never closed. This happens because: - `epollOutReady()` is a no-op when there is no pending flush. - `epollInReady()` short-circuits via `shouldBreakEpollInReady()` because input is already marked as shutdown. - The `EPOLLERR`/`EPOLLHUP` error condition is therefore never processed, and `channelInactive` is never fired. Depending on the Netty version and configuration, this results in: - **Stale channels**: The connection is never closed or deregistered. An unauthenticated remote attacker can repeat the sequence to accumulate stale connections, exhausting file descriptors, memory, or connection-count limits. - **CPU busy-loop**: In code paths where `clearEpollIn0()` is not called during the `ChannelInputShutdownReadComplete` event, `epoll_wait` returns immediately on every iteration for the affected fd, causing 100% CPU utilization on the event loop thread and starving all other connections multiplexed on it. ## Mitigation - Upgrade to 4.2.13.Final when released (or build from the `4.2` branch at commit [`0ec3d97`](https://github.com/netty/netty/commit/0ec3d97fab376e243d328ac95fbd288ba0f6e22d)). - If upgrading is not immediately possible, configure idle timeouts on connections to limit the lifetime of stale channels. ## References - Issue: https://github.com/netty/netty/issues/16683 - Fix: https://github.com/netty/netty/pull/16689