CVE-2026-93563
Published:September 18, 2026
Updated:October 09, 2026
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.
Affected Packages
https://github.com/netty/netty.git (GITHUB):
Affected version(s) >=netty-4.2.0.Final <netty-4.2.18.FinalFix Suggestion:
Update to version netty-4.2.18.Finalhttps://github.com/netty/netty.git (GITHUB):
Affected version(s) >=netty-4.1.0.Final <netty-4.1.138.FinalFix Suggestion:
Update to version netty-4.1.138.Finalio.netty:netty-codec-smtp (JAVA):
Affected version(s) >=4.2.0.Final <4.2.18.FinalFix Suggestion:
Update to version 4.2.18.Finalio.netty:netty-codec-smtp (JAVA):
Affected version(s) >=4.1.0.Final <4.1.138.FinalFix Suggestion:
Update to version 4.1.138.Finalio.netty:netty-all (JAVA):
Affected version(s) >=4.1.7.Final <4.1.138.FinalFix Suggestion:
Update to version 4.1.138.FinalRelated Resources (3)
Do you need more information?
Contact UsCVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
EPSS
Base Score:
0.33