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CVE-2026-49844 (GCVE-0-2026-49844)

Vulnerability from cvelistv5 – Published: 2026-07-10 21:14 – Updated: 2026-09-17 18:37
VLAI
Title
Apache Log4j API: Improper serialization of non-finite floating-point values in MapMessage.asJson()
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.
Severity
6.3 (Medium)
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
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-14 13:56 UTC
CWE
  • CWE-116 - Improper Encoding or Escaping of Output
Assigner
References
Impacted products
Vendor Product Version CPE status
Apache Software Foundation Apache Log4j API Affected: 2.13.1 , < 2.25.5 (maven)
Affected: 2.26.0 , < 2.26.1 (maven)
Affected: 3.0.0-alpha1 , ≤ 3.0.0-beta2 (maven)
    cpe:2.3:a:apache:log4j_api:*:*:*:*:*:*:*:*
Create a notification for this product.
Credits
Himanshu Anand
Show details on NVD website
To clipboard 

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                  "value": "\u003cp\u003eImproper encoding of non-finite floating-point values during \u003ccode\u003eMapMessage\u003c/code\u003e 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.\u003c/p\u003e\u003cp\u003eThe fix for CVE-2026-34481 did not cover all code paths: when a \u003ccode\u003eMapMessage\u003c/code\u003e contains a non-finite IEEE 754 value (\u003ccode\u003eNaN\u003c/code\u003e, \u003ccode\u003eInfinity\u003c/code\u003e, or \u003ccode\u003e-Infinity\u003c/code\u003e), \u003ccode\u003eMapMessage.asJson()\u003c/code\u003e emits the corresponding bare token. RFC 8259 does not permit these tokens, so a conformant parser rejects the resulting document.\u003c/p\u003e\u003cp\u003eThe defect is reachable only when both of the following conditions hold:\u003c/p\u003e\u003cul\u003e\u003cli\u003eThe application uses the \u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message\"\u003e\u003ccode\u003emessage\u003c/code\u003e resolver\u003c/a\u003e of \u003ccode\u003eJsonTemplateLayout\u003c/code\u003e or any other layout that relies on \u003ccode\u003eMapMessage.asJson()\u003c/code\u003e or \u003ccode\u003eMapMessage.getFormattedMessage(new String[]{\"JSON\"})\u003c/code\u003e.\u003c/li\u003e\u003cli\u003eThe application logs a \u003ccode\u003eMapMessage\u003c/code\u003e that contains an attacker-controlled floating-point value.\u003c/li\u003e\u003c/ul\u003e\u003cp\u003eAn 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.\u003c/p\u003e\u003cp\u003eUsers 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.\u003c/p\u003e"
                }
              ],
              "value": "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.\n\nThe 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.\n\nThe defect is reachable only when both of the following conditions hold:\n\n  *  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\"}).\n  *  The application logs a MapMessage that contains an attacker-controlled floating-point value.\n\n\nAn 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.\n\nUsers 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."
            }
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            {
              "cvssV4_0": {
                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "PRESENT",
                "attackVector": "NETWORK",
                "baseScore": 6.3,
                "baseSeverity": "MEDIUM",
                "privilegesRequired": "NONE",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "NONE",
                "subIntegrityImpact": "LOW",
                "userInteraction": "NONE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "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",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "NONE",
                "vulnIntegrityImpact": "NONE",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
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              "format": "CVSS",
              "scenarios": [
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                  "lang": "en",
                  "value": "GENERAL"
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              ]
            },
            {
              "other": {
                "content": {
                  "text": "moderate"
                },
                "type": "Textual description of severity"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-116",
                  "description": "CWE-116 Improper Encoding or Escaping of Output",
                  "lang": "en",
                  "type": "CWE"
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              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-07-10T21:14:59.111Z",
            "orgId": "f0158376-9dc2-43b6-827c-5f631a4d8d09",
            "shortName": "apache"
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            {
              "tags": [
                "related"
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              "url": "https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message"
            },
            {
              "tags": [
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              "url": "https://github.com/apache/logging-log4j2/pull/4163"
            },
            {
              "tags": [
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              "url": "https://logging.apache.org/cyclonedx/vdr.xml"
            },
            {
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://logging.apache.org/security.html#CVE-2026-49844"
            }
          ],
          "source": {
            "discovery": "EXTERNAL"
          },
          "title": "Apache Log4j API: Improper serialization of non-finite floating-point values in MapMessage.asJson()",
          "x_generator": {
            "engine": "Vulnogram 0.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "f0158376-9dc2-43b6-827c-5f631a4d8d09",
        "assignerShortName": "apache",
        "cveId": "CVE-2026-49844",
        "datePublished": "2026-07-10T21:14:59.111Z",
        "dateReserved": "2026-06-01T20:15:42.977Z",
        "dateUpdated": "2026-09-17T18:37:58.088Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.