{"schemaVersion":3,"id":"CVE-2026-105239","aliases":["UBUNTU-CVE-2026-105239","DEBIAN-CVE-2026-105239"],"status":"published","duplicateOf":null,"title":null,"description":"Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net.\n\nA NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. 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":"2026-10-06T19:46:33.357Z","modified":"2026-10-07T06:11:55.256Z","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 · 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Neutralization of Null Byte or NUL Character","description":"The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes NUL characters or null bytes when they are sent to a downstream component.","type":"weakness","status":"Incomplete","abstraction":"Variant","likelihoodOfExploit":null,"url":"https://cwe.mitre.org/data/definitions/158.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, < dc5855a0720c91590fd7a81d729ea01fdd69e000","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 1.2.9, < 3.5.0 | ≥ 02e1e115435888485f2e28b414d267e39e799e07, < dc5855a0720c91590fd7a81d729ea01fdd69e000","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/dc5855a0720c91590fd7a81d729ea01fdd69e000","label":"github.com/apache/logging-log4net/commit/dc5855a0720c91590fd7a81d729ea01fdd69e000","hostname":"github.com","tags":["Patch"]},{"url":"https://lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq","label":"lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq","hostname":"lists.apache.org","tags":["Vendor Advisory","Mailing List"]},{"url":"http://www.openwall.com/lists/oss-security/2026/10/07/14","label":"www.openwall.com/lists/oss-security/2026/10/07/14","hostname":"www.openwall.com","tags":["Mailing List","Third Party Advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-105239","label":"ubuntu.com/security/CVE-2026-105239","hostname":"ubuntu.com","tags":["REPORT"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-105239","label":"www.cve.org/CVERecord?id=CVE-2026-105239","hostname":"www.cve.org","tags":["REPORT"]},{"url":"https://lists.apache.org/thread/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq","label":"lists.apache.org/thread/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq","hostname":"lists.apache.org","tags":["REPORT"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-105239","label":"security-tracker.debian.org/tracker/CVE-2026-105239","hostname":"security-tracker.debian.org","tags":["Advisory"]}],"lineage":{"upstream":[],"downstream":[],"duplicates":[],"related":[]},"timeline":[{"kind":"published","date":"2026-10-06T19:46:33.357Z","label":"Published","detail":"Vulnerability first disclosed.","source":null},{"kind":"modified","date":"2026-10-07T06:11:55.256Z","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":"2026-10-19T08:21:37.544Z","stale":false,"partial":false}}