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CVE-2026-49844

5.9 · MEDIUM

Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API produces output that is not valid JSON.

Published Jul 10, 2026CWE-116EPSS 0.81%

Overview

CVE-2026-49844 is a medium-severity vulnerability. It was published on July 10, 2026 and has a CVSS 3.1 base score of 5.9 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

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 attac

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/apache/logging-log4j2/pull/4163Reflogging.apache.org/cyclonedx/vdr.xmlReflogging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-messageReflogging.apache.org/security.html#CVE-2026-49844

How CyberStrike helps

Frequently asked questions

What is CVE-2026-49844?

CVE-2026-49844 is a medium-severity vulnerability. It was published on July 10, 2026 and has a CVSS 3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-49844?

This vulnerability has a CVSS 3.1 base score of 5.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-49844?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-49844?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-49844 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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