{"id":"CVE-2026-105243","aliases":["DEBIAN-CVE-2026-105243","EUVD-2026-93869","GHSA-j8mm-w573-8v6c","UBUNTU-CVE-2026-105243"],"status":"published","title":"Apache log4net: Oversize EventLogAppender record silently discarded","description":"Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.\n\nLong 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.\n\nThis issue affects Apache log4net: from 1.2.9 before 3.5.0.\n\nUsers are recommended to upgrade to version 3.5.0, which fixes the issue.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00807,"percentile":0.5727,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-778"],"published":"2026-10-06T19:51:25Z","modified":"2026-10-28T02:30:50Z","affected":[{"source":"osv","ecosystem":"Debian:13","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-10","1.2.10+dfsg-9"]},{"source":"osv","ecosystem":"Debian:14","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-10","1.2.10+dfsg-9"]},{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-6","1.2.10+dfsg-7","1.2.10+dfsg-7ubuntu0.16.04.1"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-7","1.2.10+dfsg-7ubuntu0.18.04.1"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-7","1.2.10+dfsg-7ubuntu0.20.04.1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-8"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-8","1.2.10+dfsg-9"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-9build1","1.2.10+dfsg-10"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"log4net","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.10+dfsg-9","1.2.10+dfsg-9build1"]}],"products":[{"vendor":"apache","product":"log4net"},{"vendor":"apache software foundation","product":"apache log4net"}],"references":[{"url":"https://github.com/apache/logging-log4net/pull/315","tags":["patch","Patch","fix","report"]},{"url":"https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed","tags":["patch","Patch","fix"]},{"url":"https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp","tags":["vendor-advisory","Mailing List","Vendor Advisory","advisory"]},{"url":"http://www.openwall.com/lists/oss-security/2026/10/07/17","tags":["Mailing List","Third Party Advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-105243","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-j8mm-w573-8v6c"},{"url":"https://nuget.org/packages","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/105xxx/CVE-2026-105243.json","tags":["advisory"]},{"url":"https://gitbox.apache.org/repos/asf/logging-log4net.git","tags":["package"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-105243","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-105243","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-105243","tags":["report"]},{"url":"https://lists.apache.org/thread/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-105243","title":"Apache log4net: Oversize EventLogAppender record silently discarded","description":"Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.\n\nLong 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.\n\nThis issue affects Apache log4net: from 1.2.9 before 3.5.0.\n\nUsers are recommended to upgrade to version 3.5.0, which fixes the issue.","status":"published","published":"2026-10-06T19:51:25.116Z","modified":"2026-10-07T14:49:41.976Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-778"],"updated_at":"2026-11-02T14:19:57.100857Z"}],"euvd":[{"id":"EUVD-2026-93869","description":"Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.\n\nLong 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.\n\nThis issue affects Apache log4net: from 1.2.9 before 3.5.0.\n\nUsers are recommended to upgrade to version 3.5.0, which fixes the issue.","status":"published","published":"2026-10-06T19:51:25Z","modified":"2026-10-07T14:49:41Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T17:27:35.164729Z"}],"ghsa":[{"id":"GHSA-j8mm-w573-8v6c","title":"Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.\n\nLong messages were...","description":"Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.\n\nLong 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.\n\nThis issue affects Apache log4net: from 1.2.9 before 3.5.0.\n\nUsers are recommended to upgrade to version 3.5.0, which fixes the issue.","status":"published","published":"2026-10-06T21:31:59Z","modified":"2026-10-07T09:32:19Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-778"],"updated_at":"2026-11-02T15:12:53.496212Z"}],"nvd":[{"id":"CVE-2026-105243","description":"Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.\n\nLong 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.\n\nThis issue affects Apache log4net: from 1.2.9 before 3.5.0.\n\nUsers are recommended to upgrade to version 3.5.0, which fixes the issue.","status":"published","published":"2026-10-06T20:17:16.167Z","modified":"2026-10-09T15:26:03.43Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-778"],"updated_at":"2026-11-02T14:12:54.809359Z"}],"osv":[{"id":"CVE-2026-105243","title":"Apache log4net: Oversize EventLogAppender record silently discarded","description":"Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.\n\nLong 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.\n\nThis issue affects Apache log4net: from 1.2.9 before 3.5.0.\n\nUsers are recommended to upgrade to version 3.5.0, which fixes the issue.","status":"published","published":"2026-10-06T19:51:25.116Z","modified":"2026-10-28T02:30:50.742686711Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-778"],"updated_at":"2026-11-02T15:44:54.583213Z"},{"id":"DEBIAN-CVE-2026-105243","description":"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.","status":"published","published":"2026-10-06T20:17:16.167Z","modified":"2026-10-10T09:47:47.308254516Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T15:45:48.903138Z"},{"id":"UBUNTU-CVE-2026-105243","description":"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.","status":"published","published":"2026-10-06T20:17:00Z","modified":"2026-10-17T12:58:42.822531616Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T16:55:59.130573Z"}]}}