HighCVE-2026-34481

    Apache Log4j JSON Template Layout: Improper Encoding or Escaping of Output (CVE-2026-34481)

    Published Last modified Sources: BSI, Red Hat, CVE.org, OSV, Msrc Update Guide

    What is affected, what to do

    Apache Log4j's JsonTemplateLayout https://logging.apache.org/log4j/2.x/manual/json-template-layout.html , in versions up to and including 2.25.3, produces invalid JSON output when log events contain non-finite floating-point values (NaN, Infinity, or -Infinity), which are prohibited by RFC 8259. This may cause downstream log processing systems to reject or fail to index affected records. An attacker can exploit this issue only if both of the following conditions are met: * The application uses JsonTemplateLayout. * The application logs a MapMessage, or logs an object directly (e.g., via Logger.info(Object), which wraps it in an ObjectMessage), where the message contains an attacker-controlled floating-point value.

    Update Apache Log4j JSON Template Layout to version 2.25.4.

    Affected
    • Apache Log4j JSON Template Layout lt 2.14.0..2.25.4
    • Apache Log4j JSON Template Layout lte 3.0.0-alpha1..3.0.0-beta3
    Fixed in
    • Apache Log4j JSON Template Layout 2.25.4

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: BSI, Red Hat, CVE.org, OSV, Msrc Update Guide

    0.7 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 52.6

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    80.62 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    6.3
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.7 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    52.6
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-116

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    Apache Log4j's JsonTemplateLayout https://logging.apache.org/log4j/2.x/manual/json-template-layout.html , in versions up to and including 2.25.3, produces invalid JSON output when log events contain non-finite floating-point values (NaN, Infinity, or -Infinity), which are prohibited by RFC 8259. This may cause downstream log processing systems to reject or fail to index affected records. An attacker can exploit this issue only if both of the following conditions are met: * The application uses JsonTemplateLayout. * The application logs a MapMessage, or logs an object directly (e.g., via Logger.info(Object), which wraps it in an ObjectMessage), where the message contains an attacker-controlled floating-point value. Users are advised to upgrade to Apache Log4j JSON Template Layout 2.25.4, which corrects this issue. Note: The fix released in version 2.25.4 did not cover all affected code paths. CVE-2026-49844 was assigned to the remaining issue, which concerns the MapMessage.asJson() serialization in Apache Log4j API and is fixed in versions 2.25.5 and 2.26.1.

    Source: BSI WID Portal, BSI CSAF, redhat_csaf, cvelistv5, OSV (Open Source Vulnerabilities), Microsoft Security Update Guide, NVD (NIST), CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    Apache Software FoundationApache Log4j JSON Template Layout
    • 2.14.0 – < 2.25.4
    • 3.0.0-alpha1 – ≤ 3.0.0-beta3
    • 2.25.4
    • —
    apachelog4j
    • 3.0.0
    • 2.14.0 – < 2.25.4
    • —
    • 2.25.4
    IBMOperational Decision Manager
    • <8.12.0.1 IF039
    • <8.11.1 IF055
    • <8.11.0.1 IF056
    • <9.5.0.1 IF010
    • <9.0.0.1 IF025
    • —
    • —
    • —
    • —
    • —
    OracleCommunications
    • 15.0.0.0.0
    • 7.5.0
    • 8.0.0
    • 15.0.1.0.0
    • 26.1.202
    • 7.7.0
    • 25.1.100
    • 47.0.0.2.0
    • 7.0.0
    • 6
    • 6.1
    • 15.1.0.0.0
    • 7.8.0
    • 15.2.0.0.0
    • 24.2.4-25.2.000
    • 7.5.1
    • 25.2.100
    • 8.0-8.1
    • 8.0.1
    • 7.3.6
    • 7.6.0
    • 14
    • 25.1.200
    • 7.4.0
    • 6.1.1-7.0.0
    • 25.2.200
    • 11
    • 26.1.200
    • 25.2.202
    • 25.2.201
    • 8.0-8.3
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
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    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    OracleConstruction and Engineering
    • 25.12.0-25.12.6
    • 24.12.0-24.12.14
    • 21.12.0.0-21.12.21.8
    • 23.12.0-23.12.19
    • 22.12.0.0-22.12.21.2
    • —
    • —
    • —
    • —
    • —
    OracleEnterprise Manager
    • 24.1
    • 13.5
    • 13.5.1.0.0-13.5.6.0.0
    • —
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-116Improper Encoding or Escaping of Output

      Class

      The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

      Entry at MITRE CWE-116

    References & sources

    • NVD (NIST)vuln/detail/CVE-2026-34481advisory
    • github.comapache/logging-log4j2/pull/4080web, Patch, Issue tracking
    • github.comapache/logging-log4j2package
    • lists.apache.orgthread/n34zdv00gbkdbzt2rx9rf5mqz6lhopcvweb, Vendor advisory, Mailing list, Vendor advisory
    • logging.apache.orgcyclonedx/vdr.xmlweb, Vendor advisory, Product
    • logging.apache.orglog4j/2.x/manual/json-template-layout.htmlweb, related, Technical description
    • logging.apache.orgsecurity.htmlweb, Vendor advisory, Vendor advisory
    • openwall.comlists/oss-security/2026/04/10/10web, Mailing list, Third-party advisory

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    One NVD translation into another language is hidden.

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