CVE-2026-49844 (Medium) detected in log4j-api-2.24.3.jar, log4j-api-2.24.1.jar

[mend-bolt-for-github]

CVE-2026-49844 - Medium Severity Vulnerability

Vulnerable Libraries - log4j-api-2.24.3.jar, log4j-api-2.24.1.jar

log4j-api-2.24.3.jar

The logging API of the Log4j project. Library and application code can log through this API. It contains a simple built-in implementation (`SimpleLogger`) for trivial use cases. Production applications are recommended to use Log4j API in combination with a fully-fledged implementation, such as Log4j Core.

Library home page: https://logging.apache.org/log4j/2.x/

Sample Path to Dependency File: /hapi-fhir-spring-boot/hapi-fhir-spring-boot-samples/hapi-fhir-spring-boot-sample-server-jersey/pom.xml

Path to vulnerable library: /hapi-fhir-spring-boot/hapi-fhir-spring-boot-samples/hapi-fhir-spring-boot-sample-server-jersey/pom.xml,/hapi-fhir-spring-boot/hapi-fhir-spring-boot-starter/pom.xml,/hapi-fhir-spring-boot/hapi-fhir-spring-boot-samples/hapi-fhir-spring-boot-sample-client-apache/pom.xml,/hapi-fhir-spring-boot/hapi-fhir-spring-boot-samples/hapi-fhir-spring-boot-sample-client-okhttp/pom.xml,/hapi-fhir-spring-boot/hapi-fhir-spring-boot-samples/hapi-fhir-spring-boot-sample-client-okhttp/pom.xml

Dependency Hierarchy:

• spring-boot-starter-web-3.4.11.jar (Root Library)
  • spring-boot-starter-3.4.11.jar
    • spring-boot-starter-logging-3.4.11.jar
      • log4j-to-slf4j-2.24.1.jar
        • ❌ log4j-api-2.24.3.jar (Vulnerable Library)

log4j-api-2.24.1.jar

The logging API of the Log4j project. Library and application code can log through this API. It contains a simple built-in implementation (`SimpleLogger`) for trivial use cases. Production applications are recommended to use Log4j API in combination with a fully-fledged implementation, such as Log4j Core.

Library home page: https://logging.apache.org/log4j/2.x/

Sample Path to Dependency File: /hapi-fhir-jpaserver-uhnfhirtest/pom.xml

Path to vulnerable library: /hapi-fhir-jpaserver-uhnfhirtest/pom.xml,/hapi-fhir-jpaserver-base/pom.xml,/hapi-tinder-test/pom.xml,/hapi-fhir-jpaserver-test-utilities/pom.xml,/hapi-fhir-jpaserver-hfql/pom.xml,/hapi-fhir-cli/hapi-fhir-cli-app/pom.xml,/hapi-fhir-cli/hapi-fhir-cli-api/pom.xml,/hapi-fhir-docs/pom.xml,/hapi-fhir-jpaserver-ips/pom.xml,/hapi-fhir-jpaserver-test-utilities/pom.xml

Dependency Hierarchy:

• hapi-fhir-cli-api-8.11.2-SNAPSHOT.jar (Root Library)
  • hapi-fhir-jpaserver-base-8.11.2-SNAPSHOT.jar
    • log4j-to-slf4j-2.24.1.jar
      • ❌ log4j-api-2.24.1.jar (Vulnerable Library)

Found in base branch: master

Vulnerability Details

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.

Publish Date: 2026-07-10

URL: CVE-2026-49844

CVSS 3 Score Details (5.8)

Base Score Metrics:

• Exploitability Metrics:
  • Attack Vector: Network
  • Attack Complexity: Low
  • Privileges Required: None
  • User Interaction: None
  • Scope: Changed
• Impact Metrics:
  • Confidentiality Impact: None
  • Integrity Impact: Low
  • Availability Impact: None

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: https://logging.apache.org/security.html#CVE-2026-49844

Release Date: 2026-07-10

Fix Resolution: org.apache.logging.log4j:log4j-api:2.25.5,org.apache.logging.log4j:log4j-api:2.26.1

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