Improper Encoding or Escaping of Output in Apache Log4j - CVE-2026-34481
Published: April 28, 2026
Vulnerability identifier: #VU128403
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-2026-34481
CWE-ID: CWE-116
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 cause downstream log processing systems to reject or fail to index affected records.
The vulnerability exists due to improper serialization of non-finite floating-point values in JsonTemplateLayout when processing log events containing a MapMessage with an attacker-controlled floating-point value. A remote attacker can supply a non-finite floating-point value to cause downstream log processing systems to reject or fail to index affected records.
Exploitation is possible only if the application uses JsonTemplateLayout and logs a MapMessage containing the attacker-controlled value.
How to mitigate CVE-2026-34481
Install security update from vendor's website.