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Fencer Intel
medium 5.9

CVE-2026-49844 json

Apache Log4j API: Improper serialization of non-finite floating-point values in MapMessage.asJson()

published 3mo ago modified 15d ago also EUVD-2026-43102 , GHSA-qv9r-c865-cp47

cvss
5.9
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 48%
public exploits
0
none known

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 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.

Patch / fix

  • maven org.apache.logging.log4j:log4j-api 2.25.5, 2.26.1
  • Apache Software Foundation Apache Log4j API 2.25.5, 2.26.1

Is CVE-2026-49844 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-49844 updated cvss 5.9

org.apache.logging.log4j/log4j-api: Apache Log4j API: Malformed JSON output due to improper encoding of floating-point values

  • Red Hat Cryostat 4 log4j-api 2.25.4 Red Hat OpenShift Serverless openshift-serverless-1/kn-eventing-integrations-aws-s3-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-sns-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-sqs-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-s3-source-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-sqs-source-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-ddb-streams-source-rhel9 Red Hat AI Inference Server rhaii/vllm-gaudi-rhel9, rhaiis/vllm-cuda-rhel9 Red Hat AMQ Broker 7 log4j-api 2.25.4 Red Hat AMQ Clients log4j-api 2.25.4 Red Hat build of Apache Camel - HawtIO 4 log4j-api 2.25.4
    affected: workaround, no fix available “Fix deferred”
  • Red Hat build of Apache Camel 4 for Quarkus 3 log4j-api 2.25.4
    affected: workaround, no fix available
  • Red Hat build of Apache Camel for Spring Boot 4 log4j-api 2.25.4 Red Hat Data Grid 8 log4j-api 2.25.4 Red Hat Enterprise Linux 8 resteasy, resteasy-javadoc Red Hat Enterprise Linux 9 resteasy, pki-resteasy-core, pki-resteasy-client, pki-resteasy-jackson2-provider, pki-resteasy-servlet-initializer Red Hat Enterprise Linux AI (RHEL AI) 3 bazel7 7.7.1-1.el9ai, bazel8 8.6.0-1.el9ai, rhelai3/bootc-gaudi-rhel9 Red Hat JBoss Enterprise Application Platform 7 log4j-api 2.25.4, eap74-els-openjdk8-openshift-rhel8, eap74-els-openjdk11-openshift-rhel8, eap74-els-openjdk17-openshift-rhel8, jboss-eap-7-eap74-els-openjdk11-openshift-rhel8, jboss-eap-7-eap74-els-openjdk17-openshift-rhel8
    +9 more products
    Red Hat JBoss Enterprise Application Platform 8 log4j-api 2.25.4 Red Hat JBoss Enterprise Application Platform Expansion Pack log4j-api 2.25.4 Red Hat JBoss Web Server 5 jws5-jboss-logging Red Hat Offline Knowledge Portal offline-knowledge-portal/rhokp-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-modelmesh-rhel9, rhoai/odh-vllm-gaudi-rhel9, rhoai/odh-spark-operator-rhel9, rhoai/odh-th06-cpu-torch210-py312-rhel9, rhoai/odh-th06-cpu-torch291-py312-rhel9, rhoai/odh-th06-rocm64-torch291-py312-rhel9, +14 more Red Hat OpenShift Dev Spaces devspaces/openvsx-rhel9, devspaces/pluginregistry-rhel9 Red Hat Single Sign-On 7 log4j-api 2.25.4 Red Hat streams for Apache Kafka 2 log4j-api 2.25.4 Red Hat streams for Apache Kafka 3 log4j-api 2.25.4
    affected: workaround, no fix available “Fix deferred”
  • Red Hat build of Apicurio Registry 3 log4j-api 2.25.4 Red Hat Fuse 7 log4j-api 2.25.4
    under investigation

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3mo ago

Exploit prediction

0.60% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
maven org.apache.logging.log4j:log4j-api
>=2.13.1, <2.25.5
>=2.26.0, <2.26.1
2.25.5
2.26.1

Affected products

  • Apache Software Foundation Apache Log4j API

Classification

Weakness
  • CWE-116 Improper Encoding or Escaping of Output
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.