CVE-2026-93563 Denial of service in Red Hat Fuse 7
A remote attacker can cause a denial of service by sending unbounded multi-line SMTP responses, exhausting memory in applications using the Netty SMTP codec.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-93563?
CVE-2026-93563 is a high-severity denial of service vulnerability in Red Hat Fuse 7, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A flaw was found in Netty's `SmtpResponseDecoder` component. A remote attacker, acting as a malicious or man-in-the-middle (MITM) SMTP server, could exploit this by sending a specially crafted, unbounded multi-line SMTP response without a terminator. This vulnerability leads to unbounded memory accumulation within the client's Java Virtual Machine (JVM) heap, causing an `OutOfMemoryError` and a denial of service (DoS) due to a process crash.
Weakness: CWE-1035
Which versions are affected by CVE-2026-93563?
How do I fix CVE-2026-93563?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-93563 being exploited?
There is no known exploitation of CVE-2026-93563 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-93563, GHSA-mv3r-x43m-8mr7, UBUNTU-CVE-2026-93563.