Improper Output Neutralization for Logs in Apache Log4j - CVE-2026-34478
Published: April 28, 2026
Vulnerability identifier: #VU128400
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-34478
CWE-ID: CWE-117
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Apache Foundation
Affected software:
Apache Log4j
Apache Log4j
Detailed vulnerability description
The vulnerability allows a remote attacker to inject arbitrary log entries.
The vulnerability exists due to improper neutralization of CRLF sequences in Rfc5424Layout when processing logged data with direct Rfc5424Layout configuration using TCP framing. A remote attacker can supply specially crafted input containing CRLF sequences to inject arbitrary log entries.
Only users of stream-based syslog services who configure Rfc5424Layout directly are affected. Users of the SyslogAppender are not affected.
How to mitigate CVE-2026-34478
Install security update from vendor's website.