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DEBIAN-CVE-2026-40021

Type: advisorySource: OSV1 source record

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.

Announced Source revision 1
Original source ↗

DEBIAN-CVE-2026-40021

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: osv:DEBIAN-CVE-2026-40021

log4net

Source reference: /affected/0/package/name

Affected versions
1.2.10+dfsg-10

Source reference: /affected/0/versions

1.2.10+dfsg-9

Source reference: /affected/0/versions

Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

log4net

Source reference: /affected/1/package/name

Affected versions
1.2.10+dfsg-9

Source reference: /affected/1/versions

Fixed versions
1.2.10+dfsg-10

Source reference: /affected/1/ranges

Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "ranges": [
      {
        "type": "ECOSYSTEM",
        "events": [
          {
            "introduced": "0"
          }
        ]
      }
    ],
    "package": {
      "name": "log4net",
      "purl": "pkg:deb/debian/log4net?arch=source&distro=trixie",
      "ecosystem": "Debian:13"
    },
    "versions": [
      "1.2.10+dfsg-10",
      "1.2.10+dfsg-9"
    ],
    "database_specific": {
      "source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-40021.json"
    },
    "ecosystem_specific": {
      "urgency": "not yet assigned"
    }
  },
  {
    "ranges": [
      {
        "type": "ECOSYSTEM",
        "events": [
          {
            "introduced": "0"
          },
          {
            "fixed": "1.2.10+dfsg-10"
          }
        ]
      }
    ],
    "package": {
      "name": "log4net",
      "purl": "pkg:deb/debian/log4net?arch=source&distro=forky",
      "ecosystem": "Debian:14"
    },
    "versions": [
      "1.2.10+dfsg-9"
    ],
    "database_specific": {
      "source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-40021.json"
    },
    "ecosystem_specific": {
      "urgency": "not yet assigned"
    }
  }
]

Publisher severity

No explicit severity was provided.

Event
#56893 · Revision 1
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Publisher date
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