---
id: CVE-2026-93563
title: A flaw was found in Netty's `SmtpResponseDecoder` component
summary: >-
  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 …
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-1035
vendor: Red Hat
product: netty-codec-smtp
affected:
  - netty-codec-smtp (all versions)
  - netty-codec-smtp (all versions)
  - jboss-eap-7/eap74-els-openjdk11-openshift-rhel8 (all versions)
  - jboss-eap-7/eap74-els-openjdk17-openshift-rhel8 (all versions)
  - jboss-eap-7/eap74-els-openjdk8-openshift-rhel8 (all versions)
  - netty-codec-smtp (all versions)
  - netty-codec-smtp (all versions)
published: '2026-09-18'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T21:18:47.130'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-93563'
references:
  - url: 'https://access.redhat.com/security/cve/CVE-2026-93563'
    label: secalert@redhat.com
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2536976'
    label: secalert@redhat.com
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93563.json
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-93563'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-93563'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-18T19:07:42.549423Z'
ingestedAt: '2026-09-18T11:40:03.681Z'
epss: 0.00325
epssPercentile: 0.25792
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Important · affected: Red Hat build of Apache Camel for Spring Boot 4, Red Hat Fuse 7, Red Hat JBoss Enterprise Application Platform 7, Red Hat Single Sign-On 7 · no fix planned: Red Hat build of Apache Camel for Spring Boot 4, Red Hat Fuse 7, Red Hat JBoss Enterprise Application Platform 7, Red Hat Single Sign-On 7 · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93563.json)