CVE-2026-34481
HighCVSS 7.5Exploitation Probability (EPSS)
Elevated risk53th percentile - higher than 53% 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
See all- CVE-2021-45046CriticalActively exploited
The fix for CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. Attackers with control over Thread Context Map (MDC) input data when using a non-default Pattern Layout with Context Lookup (e.g., $${ctx:loginId}) or Thread Context Map pattern (%X, %mdc, %MDC) can craft malicious input using a JNDI Lookup pattern, leading to information leak and remote code execution in some environments and local code execution in all environments.
- 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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS