Medium6.3Apache Software Foundation

Medium [CVE-2026-34481 +1] Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API…

This medium-severity Apache Software Foundation advisory covers CVE-2026-34481 and CVE-2026-49844 affecting Apache Log4j API.

CVE-2026-49844 Published Jul 10, 2026Updated by vendor Jul 14, 2026

CVE-2026-34481 CVE-2026-49844

Affected products & platforms

Apache Software FoundationLog4j

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Summary

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 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.

Affected versions

through 2.25.4

Official advisory · high-confidence parse· fetched 1 month ago·verify at source

Fixed versions

2.25.5
2.26.1

Official advisory · high-confidence parse· fetched 1 month ago·verify at source

Mitigation checklist

Recommended fix / mitigation

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.

Official advisory · high-confidence parse· fetched 1 month ago·verify at source

Sources

Official and corroborating records used to build this advisory.

CVE.org CNA affected-product recordCVE.org
Structured CNA affected[] data independently confirmed the affected product scope; native advisory content remains authoritative.
CVE Program
NVD discovery recordNVD
Independent discovery and scoring cross-reference. Vendor remediation guidance takes precedence. Discovered from the machine-readable feed https://services.nvd.nist.gov/rest/json/cves/2.0; this link opens the NVD record for CVE-2026-34481 instead of the raw feed document.
NIST National Vulnerability Database

Cross-references

Validate CVE metadata against the authoritative registries.

Official resources

ASF Security — reporting & CVE process
Official documentation
The Apache Software Foundation's official security page: how ASF CVEs are published and where each project's advisories live.
Apache project downloads (fixed releases)
Official documentation
Official ASF download tree — fetch the fixed release named in this advisory from the project's directory.

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