Vulnerability intelligence

CVE-2026-49844

Apache Software Foundation Apache Log4j API CWE-116

Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API produces output that is not valid JSON. This issue affects Apache Log4j API versions 2.13.1 through 2.25.4 and version 2.26.0. The fix for CVE-2026-34481 did not cover all code paths: when a MapMessage contains a non-finite IEEE 754 value (NaN, Infinity, or -Infinity), MapMessage.asJson() emits the corresponding bare token. RFC 8259 does not permit these tokens, so a conformant parser rejects the resulting document. The defect is reachable only when both of the following conditions hold: The application uses the message resolver https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message of JsonTemplateLayout or any other layout that relies on MapMessage.asJson() or MapMessage.getFormattedMessage(new String[]{"JSON"}).

CVSS Score

6.3

Medium

EPSS — Exploit Probability

0.8%

Riskier than 56% of all CVEs · checked 2026-10-10

Exploitation

Not in CISA KEV

KEV does not include every exploited vulnerability

Remediation

Patch available

Vendor fix published