{"schemaVersion":3,"id":"CVE-2026-105243","aliases":["UBUNTU-CVE-2026-105243","DEBIAN-CVE-2026-105243"],"status":"published","duplicateOf":null,"title":null,"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.","dates":{"published":"2026-10-06T19:51:25.116Z","modified":"2026-10-07T14:49:41.976Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":5.3,"severity":"medium","version":"3.1","versionLabel":"v3.1","source":"CVE.org","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","computed":false,"selection":"backend-summary"},"metrics":[{"version":"3.1","versionLabel":"v3.1","source":"CVE.org","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","exploitability":null,"impact":null,"computed":false},{"version":"3.1","versionLabel":"v3.1","source":"OSV · Ubuntu","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","exploitability":10,"impact":2.3,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"OSV · Debian","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","exploitability":10,"impact":2.3,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.00806,"percentile":0.56068,"severity":"low","asOf":"2026-10-19T00:00:00.000Z","change":{"pp":null,"baselineDate":null,"baselineScore":null},"history":[{"date":"2026-10-07T00:00:00.000Z","score":0.00331,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00331,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00331,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00806,"percentile":0.56068}],"last30":[{"date":"2026-10-07T00:00:00.000Z","score":0.00331,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00331,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00331,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00806,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00806,"percentile":0.56068}]},"kev":{"state":"not-listed","entries":[],"listedCount":0,"totalCatalogs":3,"catalogs":[{"source":"cisa","label":"CISA","listed":false,"entry":null},{"source":"enisa","label":"ENISA","listed":false,"entry":null},{"source":"circl","label":"CIRCL","listed":false,"entry":null}]},"ransomware":{"state":"none-recorded","sources":[]},"exploits":[],"exploitCount":0,"weaknesses":[{"id":"CWE-778","name":"Insufficient Logging","description":"When a security-critical event occurs, the product either does not record the event or omits important details about the event when logging it.","type":"weakness","status":"Draft","abstraction":"Base","likelihoodOfExploit":"Medium","url":"https://cwe.mitre.org/data/definitions/778.html"}],"affected":[{"vendor":"apache software foundation","product":"apache log4net","name":"Apache Log4net","label":"apache log4net","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≥ 1.2.9, < 3.5.0","noFixRecorded":false,"fixedIn":null},{"text":"≥ 02e1e115435888485f2e28b414d267e39e799e07, < 28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 1.2.9, < 3.5.0 | ≥ 02e1e115435888485f2e28b414d267e39e799e07, < 28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed","eol":null,"hubHref":"/vendor/apache_software_foundation/apache_log4net"},{"vendor":"apache","product":"log4net","name":"log4net","label":"log4net","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≥ 1.2.9, < 3.5.0","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 1.2.9, < 3.5.0","eol":null,"hubHref":"/vendor/apache/log4net"},{"vendor":"debian","product":"log4net","name":"log4net","label":"log4net","ecosystem":"Debian","cpePart":null,"purl":"pkg:deb/debian/log4net","purlType":"deb","versions":[{"text":"All versions","noFixRecorded":true,"fixedIn":null}],"versionsText":"All versions (No fix recorded)","eol":null,"hubHref":null},{"vendor":"ubuntu","product":"log4net","name":"log4net","label":"log4net","ecosystem":"Ubuntu","cpePart":null,"purl":"pkg:deb/ubuntu/log4net","purlType":"deb","versions":[{"text":"All versions","noFixRecorded":true,"fixedIn":null}],"versionsText":"All versions (No fix recorded)","eol":null,"hubHref":null}],"affectedCount":4,"eol":{"hasEol":false,"count":0},"references":[{"url":"https://github.com/apache/logging-log4net/pull/315","label":"github.com/apache/logging-log4net/pull/315","hostname":"github.com","tags":["Patch","REPORT"]},{"url":"https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed","label":"github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed","hostname":"github.com","tags":["Patch"]},{"url":"https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp","label":"lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp","hostname":"lists.apache.org","tags":["Vendor Advisory","Mailing List"]},{"url":"http://www.openwall.com/lists/oss-security/2026/10/07/17","label":"www.openwall.com/lists/oss-security/2026/10/07/17","hostname":"www.openwall.com","tags":["Mailing List","Third Party Advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-105243","label":"ubuntu.com/security/CVE-2026-105243","hostname":"ubuntu.com","tags":["REPORT"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-105243","label":"www.cve.org/CVERecord?id=CVE-2026-105243","hostname":"www.cve.org","tags":["REPORT"]},{"url":"https://lists.apache.org/thread/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp","label":"lists.apache.org/thread/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp","hostname":"lists.apache.org","tags":["REPORT"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-105243","label":"security-tracker.debian.org/tracker/CVE-2026-105243","hostname":"security-tracker.debian.org","tags":["Advisory"]}],"lineage":{"upstream":[],"downstream":[],"duplicates":[],"related":[]},"timeline":[{"kind":"published","date":"2026-10-06T19:51:25.116Z","label":"Published","detail":"Vulnerability first disclosed.","source":null},{"kind":"modified","date":"2026-10-07T14:49:41.976Z","label":"Last modified","detail":"Vulnerability information updated.","source":null}],"risk":{"score":21,"level":"low","profile":"Default","thresholds":{"critical":75,"high":50,"medium":25,"low":10}},"meta":{"dataAsOf":"2026-10-20T05:37:32.360Z","stale":false,"partial":false}}