CVE-2026-34481

HighCVSS 7.5

Published: 10/04/2026(UTC)Updated: 11/07/2026(UTC)Translated: 14/07/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.56%

42th percentile - higher than 42% of all known CVEs

Summary

Apache Log4j JsonTemplateLayout up to version 2.25.3 produces invalid JSON output when log events contain non-finite floating-point values (NaN, Infinity, -Infinity), which violates RFC 8259. An attacker can exploit this if the application uses JsonTemplateLayout and logs a MapMessage or an object with a controlled floating-point value.

Risk Assessment

The risk is that downstream log processing systems may reject or fail to index affected records, leading to loss of log data and potentially hiding attack traces.

Recommendation

It is recommended to immediately upgrade Apache Log4j JSON Template Layout to version 2.25.4 or later. Also apply the fix for CVE-2026-49844 by upgrading to version 2.25.5 or 2.26.1.

Other vulnerabilities in Apache Log4j

CVE-2017-5645Critical
In Apache Log4j 2.x before version 2.8.2, when using the TCP socket server or UDP socket server to receive log events, a specially crafted binary payload can be sent that, when deserialized, can execute arbitrary code.

Original NVD description (English source)

Apache Log4j's JsonTemplateLayout https://logging.apache.org/log4j/2.x/manual/json-template-layout.html , in versions up to and including 2.25.3, produces invalid JSON output when log events contain non-finite floating-point values (NaN, Infinity, or -Infinity), which are prohibited by RFC 8259. This may cause downstream log processing systems to reject or fail to index affected records. An attacker can exploit this issue only if both of the following conditions are met: * The application uses JsonTemplateLayout. * The application logs a MapMessage, or logs an object directly (e.g., via Logger.info(Object), which wraps it in an ObjectMessage), where the message contains an attacker-controlled floating-point value. Users are advised to upgrade to Apache Log4j JSON Template Layout 2.25.4, which corrects this issue. Note: The fix released in version 2.25.4 did not cover all affected code paths. CVE-2026-49844 was assigned to the remaining issue, which concerns the MapMessage.asJson() serialization in Apache Log4j API and is fixed in versions 2.25.5 and 2.26.1.