{
  "cveId": "CVE-2026-40021",
  "url": "https://patchblox.com/security/cve/CVE-2026-40021",
  "summary": "CVE-2026-40021 is fixed in 5 products on 1 platform, first by DEBIAN-CVE-2026-40021, released April 10, 2026. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "log4net: Apache Log4net\u0027s  XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list  and  Xm...",
  "description": "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.  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.",
  "published": "2026-04-10T16:16:32Z",
  "severity": "medium",
  "cvss": 5.3,
  "cvssVector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
  "epss": 0.00802,
  "epssPercentile": 0.56935,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "log4net",
      "release": "Debian 14",
      "fixedVersion": "1.2.10\u002Bdfsg-10",
      "fix": "DEBIAN-CVE-2026-40021",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-40021",
      "released": "2026-04-10T16:16:32Z"
    },
    {
      "platform": "linux",
      "product": "log4net",
      "release": "Fedora 43",
      "fixedVersion": "3.5.0-1.fc43",
      "fix": "FEDORA-2026-588BC7E01C",
      "url": "https://patchblox.com/security/fix/linux/fedora-2026-588bc7e01c",
      "released": "2026-10-07T18:56:22Z"
    },
    {
      "platform": "linux",
      "product": "log4net-devel",
      "release": "Fedora 43",
      "fixedVersion": "3.5.0-1.fc43",
      "fix": "FEDORA-2026-588BC7E01C",
      "url": "https://patchblox.com/security/fix/linux/fedora-2026-588bc7e01c",
      "released": "2026-10-07T18:56:22Z"
    },
    {
      "platform": "linux",
      "product": "nant",
      "release": "Fedora 43",
      "fixedVersion": "1:0.92-43.fc43",
      "fix": "FEDORA-2026-588BC7E01C",
      "url": "https://patchblox.com/security/fix/linux/fedora-2026-588bc7e01c",
      "released": "2026-10-07T18:56:22Z"
    },
    {
      "platform": "linux",
      "product": "nant-devel",
      "release": "Fedora 43",
      "fixedVersion": "1:0.92-43.fc43",
      "fix": "FEDORA-2026-588BC7E01C",
      "url": "https://patchblox.com/security/fix/linux/fedora-2026-588bc7e01c",
      "released": "2026-10-07T18:56:22Z"
    },
    {
      "platform": "linux",
      "product": "nant-docs",
      "release": "Fedora 43",
      "fixedVersion": "1:0.92-43.fc43",
      "fix": "FEDORA-2026-588BC7E01C",
      "url": "https://patchblox.com/security/fix/linux/fedora-2026-588bc7e01c",
      "released": "2026-10-07T18:56:22Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-09T13:31:49Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}