FKIE_CVE-2026-40021

Vulnerability from fkie_nvd - Published: 2026-04-10 16:16 - Updated: 2026-04-22 14:13
Severity ?
5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Summary
Apache Log4net's XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list and XmlLayoutSchemaLog4J https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list , in versions before 3.3.0, fail to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event. An attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity. Users are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.
References
security@apache.orghttps://github.com/apache/logging-log4net/pull/280Issue Tracking
security@apache.orghttps://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7Mailing List, Vendor Advisory
security@apache.orghttps://logging.apache.org/cyclonedx/vdr.xmlProduct
security@apache.orghttps://logging.apache.org/log4net/manual/configuration/layouts.htmlProduct
security@apache.orghttps://logging.apache.org/security.html#CVE-2026-40021Vendor Advisory
af854a3a-2127-422b-91ae-364da2661108http://www.openwall.com/lists/oss-security/2026/04/10/11Mailing List, Third Party Advisory
Impacted products
Vendor Product Version
apache log4net *
To clipboard 

{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "DCD2F9E8-684B-4B34-B48B-32E8225631F3",
              "versionEndExcluding": "3.3.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Apache Log4net\u0027s  XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list  and  XmlLayoutSchemaLog4J https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list , in versions before 3.3.0, fail to sanitize characters forbidden by the  XML 1.0 specification https://www.w3.org/TR/xml/#charsets  in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event.\n\nAn attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.\n\nUsers are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue."
    }
  ],
  "id": "CVE-2026-40021",
  "lastModified": "2026-04-22T14:13:45.013",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 5.3,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 1.4,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "HIGH",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 6.3,
          "baseSeverity": "MEDIUM",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "LOW",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:H/AT:N/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",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security@apache.org",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-04-10T16:16:32.420",
  "references": [
    {
      "source": "security@apache.org",
      "tags": [
        "Issue Tracking"
      ],
      "url": "https://github.com/apache/logging-log4net/pull/280"
    },
    {
      "source": "security@apache.org",
      "tags": [
        "Mailing List",
        "Vendor Advisory"
      ],
      "url": "https://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7"
    },
    {
      "source": "security@apache.org",
      "tags": [
        "Product"
      ],
      "url": "https://logging.apache.org/cyclonedx/vdr.xml"
    },
    {
      "source": "security@apache.org",
      "tags": [
        "Product"
      ],
      "url": "https://logging.apache.org/log4net/manual/configuration/layouts.html"
    },
    {
      "source": "security@apache.org",
      "tags": [
        "Vendor Advisory"
      ],
      "url": "https://logging.apache.org/security.html#CVE-2026-40021"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Mailing List",
        "Third Party Advisory"
      ],
      "url": "http://www.openwall.com/lists/oss-security/2026/04/10/11"
    }
  ],
  "sourceIdentifier": "security@apache.org",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-116"
        }
      ],
      "source": "security@apache.org",
      "type": "Secondary"
    }
  ]
}


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