{"id":"CVE-2026-105241","title":"Improper Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.\n\nContent that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, made the write throw","summary":"Improper Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.\n\nContent that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, made the write throw. Every buffered event in the…","severity":"medium","cvss":5.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","cwe":["CWE-176"],"vendor":"apache","product":"log4net","affected":["log4net >= 1.2.9, < 3.5.0"],"patched":["log4net 3.5.0"],"published":"2026-10-06","updated":"2026-10-09","sourceUpdated":"2026-10-09T15:29:42.560","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-105241","references":[{"url":"https://github.com/apache/logging-log4net/commit/4d2e10f0908199604b4326f9df6d0b43b871e333","label":"security@apache.org"},{"url":"https://github.com/apache/logging-log4net/pull/315","label":"security@apache.org"},{"url":"https://lists.apache.org/thread.html/hg8dgh3oy8bp3dhb8nsygk9kw2o401ws","label":"security@apache.org"},{"url":"http://www.openwall.com/lists/oss-security/2026/10/07/15","label":"af854a3a-2127-422b-91ae-364da2661108"}],"tags":["nvd","cve.org"],"epss":0.00824,"epssPercentile":0.57182,"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-07T14:44:42.702949Z"},"ingestedAt":"2026-10-06T20:16:42.478Z","slug":"CVE-2026-105241","body":"## Overview\n\nImproper Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.\n\nContent that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, made the write throw. Every buffered event in the batch was discarded, not only the one carrying the content, and a truncated mail could be left in the pickup directory. A party whose data reaches a log message could suppress the records of other events. Only applications that use SmtpPickupDirAppender 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.\n\n## Affected\n\n- `log4net >= 1.2.9, < 3.5.0`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `log4net 3.5.0`","depth":"sunlit","depthScore":29,"depthScoreParts":{"impact":29.2,"likelihood":0.2,"exploitation":0,"ransomware":0},"changes":[]}