CVE-2026-49844
MediumCVSS 5.9Exploitation Probability (EPSS)
Low risk47th percentile - higher than 47% of all known CVEs
Summary
Improper encoding of non-finite floating-point values in Apache Log4j API MapMessage JSON serialization produces invalid JSON. Affects versions 2.13.1 through 2.25.4 and 2.26.0, as the fix for CVE-2026-34481 missed some code paths.
Risk Assessment
An attacker can supply a non-finite value, causing malformed JSON output that may corrupt log records and disrupt downstream log ingestion and parsing.
Recommendation
Upgrade to Apache Log4j API 2.25.5 or 2.26.1, which emit RFC 8259-compliant JSON for non-finite values.
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Original NVD description (English source)
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"}). * The application logs a MapMessage that contains an attacker-controlled floating-point value. An attacker who can supply a non-finite value can cause the affected layout to emit malformed JSON, which may corrupt the enclosing log record or disrupt downstream log ingestion and parsing. Users are advised to upgrade to Apache Log4j API 2.25.5 or 2.26.1, both of which emit RFC 8259-compliant JSON for non-finite values.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

