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CVE Record

CVE-2026-34481: Apache Log4j JSON Template Layout: Improper serialization of non-finite floating-point values in JsonTemplateLayout

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.

MediumCVSS 6.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysis

Security readout for executives and security teams

This Log4j issue can make JSON-formatted logs invalid when certain unusual numeric values are logged. The main business impact is loss or rejection of log records by downstream monitoring, SIEM, or indexing systems, not direct system takeover. Risk depends on using JsonTemplateLayout and logging attacker-influenced floating-point values. Exposure is limited to Java applications using org.apache.logging.log4j:log4j-layout-template-json with JsonTemplateLayout and logging attacker-controlled floating-point values through affected message types. Treat as a focused logging reliability issue. Prioritize systems where logs support security monitoring, audit evidence, incident response, or regulated reporting, especially internet-facing services that log user-supplied numeric data. Mitigation focus: Upgrade Apache Log4j JSON Template Layout to 2.25.4 or later per Apache guidance.; Review CVE-2026-49844 and consider 2.25.5 or 2.26.1 for the related remaining issue.; Reduce logging of attacker-controlled objects or MapMessage values where practical..

Prepared

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Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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cwe · medium confidence lookup

CWE-116: User-session and phishing behavior lookup

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CVE-2026-34481 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.3 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

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1CVSS vectors
8Timeline events
2ADP providers
6Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
6.3CVSS 4.0MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N——apache

Vulnerability scoring details

Base CVSS 4.0 score

6.3Medium
CVSS 4.0 vector shape for CVE-2026-34481Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. Source timelineapache

    Vulnerability reported by Ap4sh and ethicxz

  2. Source timelineapache

    Candidate patch internally shared by Piotr P. Karwasz

  3. Source timelineapache

    Fix shared publicly by Piotr P. Karwasz as pull request #4080

  4. Source timelineapache

    Fix verified by the reporter

  5. Source timelineapache

    Log4j 2.25.4 released

  6. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  7. CVE publishedCVE Program

    The CVE record was published.

  8. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Apache Software FoundationApache Log4j JSON Template Layoutorg.apache.logging.log4j:log4j-layout-template-json, 2.14.0, 3.0.0-alpha1unaffected
Weakness

CWE details

CWE-116

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CWE-116 · source CWE mapping

Improper Encoding or Escaping of Output

Improper Encoding or Escaping of Output represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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