CVE-2026-49844

Log corruption via bare non-finite JSON tokens

Published Jul 10, 2026 · Updated Jul 10, 2026

Improper JSON encoding in Apache Log4j API affected releases allows attackers to corrupt JSON log output using non-finite values. MapMessage.asJson() and its JSON formatted-message path emit NaN and positive or negative Infinity as bare tokens instead of valid RFC 8259 values in 2.13.1 through 2.25.4, 2.26.0, and 3.0.0-alpha1 through 3.0.0-beta2. The issue is reachable only when an application uses a layout that calls either path and logs an attacker-controlled floating-point value, causing conformant downstream parsers to reject or lose the enclosing record.

CVSS severityUnavailable
Unscored
EPSS probability0.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper JSON encoding in Apache Log4j API affected releases allows attackers to corrupt JSON log output using non-finite values. MapMessage.asJson() and its JSON formatted-message path emit NaN and positive or negative Infinity as bare tokens instead of valid RFC 8259 values in 2.13.1 through 2.25.4, 2.26.0, and 3.0.0-alpha1 through 3.0.0-beta2. The issue is reachable only when an application uses a layout that calls either path and logs an attacker-controlled floating-point value, causing conformant downstream parsers to reject or lose the enclosing record.

The record

CVE
CVE-2026-49844
Published
Jul 10, 2026
Updated
Jul 10, 2026
Vendor
The Apache Software Foundation
Product
Apache Log4j API
Classifications
Unavailable
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Jul 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.13.1 <2.25.5
  2. Affected versionversion=2.26.0 <2.26.1
  3. Affected versionversion=3.0.0-alpha1 <=3.0.0-beta2

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

The Apache Software Foundation · Apache Log4j APIversion=2.13.1 <2.25.5; version=2.26.0 <2.26.1; version=3.0.0-alpha1 <=3.0.0-beta2

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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