Apache log4net: Oversize EventLogAppender record silently discarded

{
  "id": "e887d319fa5a0df31902db29f7536ff59de026e2eef2d2b243eaad75d7024d56",
  "url": "https://osv.dev/vulnerability/CVE-2026-105243",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Apache log4net: Oversize EventLogAppender record silently discarded",
    "summary": "Insufficient Logging vulnerability in the EventLogAppender of Apache log4net. Long messages were truncated to a fixed size that exceeds what the Windows Event Log accepts once the log and source names are counted, and the event log then stored nothing and reported nothing. A party whose data reaches a log message could suppress the whole record by making it long enough. Only applications on Windows that use EventLogAppender are affected. This issue affects Apache log4net: from 1.2.9 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue.",
    "evidence": "osv:CVE-2026-105243",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-105243",
      "aliases": [
        "CVE-2026-105243"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://gitbox.apache.org/repos/asf/logging-log4net.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "02e1e115435888485f2e28b414d267e39e799e07"
                },
                {
                  "fixed": "28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "02e1e115435888485f2e28b414d267e39e799e07"
                      },
                      {
                        "fixed": "28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  }
                ]
              }
            },
            {
              "repo": "https://github.com/apache/logging-log4net",
              "type": "GIT",
              "events": [
                {
                  "introduced": "18a96716af733f7c6e4956526acdcc117a1bd461"
                },
                {
                  "fixed": "f7794ae187ab2e228e1754cb478568dd305d1b32"
                },
                {
                  "fixed": "28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.2.9"
                      },
                      {
                        "fixed": "3.5.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "rc/3.4.1-preview.1",
            "rel/3.4.0",
            "rc/3.4.0-rc1",
            "rc/3.4.0-preview.1",
            "rel/3.3.2",
            "rc/3.3.2-rc1",
            "rel/3.3.1",
            "rc/3.3.1-rc1",
            "rel/3.3.0",
            "rc/3.3.0-rc1",
            "rc/3.2.0-rc1",
            "rc/temp",
            "rel/3.2.0",
            "rc/3.2.0-preview.1",
            "rel/3.1.0",
            "rc/3.1.0-rc1",
            "rel/3.0.4",
            "rc/3.0.4-rc1",
            "rc/3.0.4-preview.1",
            "rel/3.0.3",
            "rc/3.0.3-rc1",
            "rc/3.0.3-preview.1",
            "rel/3.0.2",
            "rc/3.0.2-rc1",
            "rel/3.0.1",
            "rc/3.0.1-rc1",
            "rc/3.0.1-preview.2",
            "rc/3.0.1-preview.1",
            "rel/2.x",
            "rel/2.0.17",
            "rel/2.0.16",
            "rel/2.0.15",
            "rel/2.0.14",
            "rel/2.0.13",
            "rel/2.0.12",
            "rel/2.0.11",
            "rel/2.0.10"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-105243.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:50.742686711Z",
      "provider": "osv",
      "references": [
        "https://nuget.org/packages",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/105xxx/CVE-2026-105243.json",
        "https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-105243",
        "https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed",
        "https://github.com/apache/logging-log4net/pull/315",
        "https://gitbox.apache.org/repos/asf/logging-log4net.git"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-778"
        ],
        "cna_assigner": "apache",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/105xxx/CVE-2026-105243.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-105243",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 519316,
  "published_at": "2026-10-06T19:51:25.116+00:00"
}