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.
Analysis
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Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Apache Software Foundation | Apache Log4j API | unaffected |
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Fri, 10 Jul 2026 21:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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 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. | |
| Title | Apache Log4j API: Improper serialization of non-finite floating-point values in MapMessage.asJson() | |
| First Time appeared |
Apache
Apache log4j Api |
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| Weaknesses | CWE-116 | |
| CPEs | cpe:2.3:a:apache:log4j_api:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Apache
Apache log4j Api |
|
| References |
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| Metrics |
cvssV4_0
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MITRE
Status: PUBLISHED
Assigner: apache
Published:
Updated: 2026-07-10T21:14:59.111Z
Reserved: 2026-06-01T20:15:42.977Z
Link: CVE-2026-49844
Vulnrichment
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NVD
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Redhat
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