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Public proof of conceptFix available

CVE-2026-49844

A public proof of concept exists; no exploitation attested.

  • Published2026-07-10
  • Fixed in2.26.1 · 2.25.5
  • WeaknessCWE-116

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2026-07-1022:16CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-11-03 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-49844?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-49844?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

OSV · NVD
Apache Log4j
BranchAffectedFixed in
2.26≥ 2.26.0, < 2.26.12.26.1
2.x≥ 2.13.1, < 2.25.52.25.5
2.26= 2.26.0no fix published
3.0= 3.0.0no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As apache, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • Apache Software Foundation Apache Log4j APIother versions: not affected

    package org.apache.logging.log4j:log4j-apihttps://repo.maven.apache.org/maven2

    Affected
    • ≥ 2.13.1, < 2.25.5fixed in 2.25.5maven
    • ≥ 2.26.0, < 2.26.1fixed in 2.26.1maven
    • ≥ 3.0.0-alpha1, ≤ 3.0.0-beta2no fix statedmaven

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-07-10

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • activemqCleanStartall versions · fixed in 6.2.8-r1
  • activemqCleanStartall versions · fixed in 6.2.8-r2
  • activemqCleanStartall versions · fixed in 6.3.1-r1
  • airbyte-platform-serverChainguardall versions · fixed in 2.0.0-r6
  • airbyte-server-fipsChainguardall versions · fixed in 2.0.0-r15
  • akhqWolfiall versions · fixed in 0.28.0-r6
  • akhqChainguardall versions · fixed in 0.28.0-r6
  • apache-activemq-5.19MinimOSall versions · fixed in 5.19.10-r0and 1 other package

219 more package ranges on OSV.dev

Vendor advisories

  • CVE-2026-49844 Red Hat Product Security65 known affected

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

    log4j-api as a component of Cryostat 4 · openshift-serverless-1/kn-eventing-integrations-aws-ddb-streams-source-rhel9 as a component of OpenShift Serverless · openshift-serverless-1/kn-eventing-integrations-aws-s3-sink-rhel9 as a component of OpenShift Serverless · +62 more

Full record on NVD

Fix

  1. Update Apache Log4j to 2.26.1 · 2.25.5
  2. Workaround from the vendor Red Hat Product Security CVE-2026-49844 · 65 productsMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
  3. No fix available, says the vendor Red Hat Product Security CVE-2026-49844 · 64 productsFix deferred
  4. No fix available, says the vendor Red Hat Product Security CVE-2026-49844 · 1 productAffected

Advisories and patches

Detection

read 2026-11-03 22:42 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiedxiaoqiMikko/log4j-check
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS 4.0 vector
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
Published
2026-07-10
Last Modified
2026-10-25
NVD status
Analyzed
GitHub Advisory
GHSA-qv9r-c865-cp47

Frequently asked questions

What is CVE-2026-49844?

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.

Is CVE-2026-49844 actively exploited?

Active exploitation of CVE-2026-49844 has not been confirmed. Its EPSS score was 0.6% on 2026-11-03, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-49844?

CVE-2026-49844 has a CVSS v3 base score of 5.9 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N.

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