{"id":"EUVD-2026-21488","enisaUuid":"c1e462b1-b3cd-3659-bf4b-2b8c95b43e5b","description":"Apache Log4net\u0027s  XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list  and  XmlLayoutSchemaLog4J https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list , in versions before 3.3.0, fail to sanitize characters forbidden by the  XML 1.0 specification https://www.w3.org/TR/xml/#charsets  in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event.\n\nAn attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.\n\nUsers are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.","datePublished":"Apr 10, 2026, 3:44:17 PM","dateUpdated":"Apr 10, 2026, 5:35:01 PM","baseScore":6.3,"baseScoreVersion":"4.0","baseScoreVector":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N","references":"https://github.com/apache/logging-log4net/pull/280\nhttps://logging.apache.org/security.html#CVE-2026-40021\nhttps://logging.apache.org/cyclonedx/vdr.xml\nhttps://logging.apache.org/log4net/manual/configuration/layouts.html\nhttps://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7\n","aliases":"CVE-2026-40021\nGHSA-4f7c-pmjv-c25w\n","assigner":"apache","epss":0.77,"enisaIdProduct":[{"id":"b045f414-2d94-368a-bbcd-18ad50ec19b2","product":{"name":"Apache log4net","vendor":{"name":"Apache Software Foundation"}},"product_version":"0 \u003c3.3.0"}],"enisaIdVendor":[{"id":"696cbd39-1a7a-3a49-802d-169a0083ecc9","vendor":{"name":"Apache Software Foundation"}}],"enisaIdVulnerability":[{"id":"0a5612be-c96f-38a9-a764-5b7d26313287","vulnerability":{"id":"GHSA-4f7c-pmjv-c25w","description":"Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters","datePublished":"Apr 10, 2026, 6:31:18 PM","dateUpdated":"Apr 27, 2026, 4:18:56 PM","baseScore":0.0,"references":"https://nvd.nist.gov/vuln/detail/CVE-2026-40021\nhttps://github.com/apache/logging-log4net/pull/280\nhttps://github.com/apache/logging-log4net\nhttps://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7\nhttps://logging.apache.org/cyclonedx/vdr.xml\nhttps://logging.apache.org/log4net/manual/configuration/layouts.html\nhttps://logging.apache.org/security.html#CVE-2026-40021\nhttp://www.openwall.com/lists/oss-security/2026/04/10/11\n","enisa_id":"EUVD-2026-21488\n","aliases":"GHSA-4f7c-pmjv-c25w\nCVE-2026-40021\n","epss":0.0,"dataProcessed":"Oct 25, 2026, 1:55:10 AM","vulnerabilityProduct":[],"vulnerabilityVendor":[]}},{"id":"37d9eef9-5e1f-36c0-b06a-0e7b288f95c9","vulnerability":{"id":"CVE-2026-40021","description":"Apache Log4net\u0027s  XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list  and  XmlLayoutSchemaLog4J https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list , in versions before 3.3.0, fail to sanitize characters forbidden by the  XML 1.0 specification https://www.w3.org/TR/xml/#charsets  in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event.\n\nAn attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.\n\nUsers are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.","datePublished":"Apr 10, 2026, 3:44:17 PM","dateUpdated":"Apr 10, 2026, 5:35:01 PM","status":"PUBLISHED","baseScore":6.3,"baseScoreVersion":"4.0","baseScoreVector":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N","references":"https://github.com/apache/logging-log4net/pull/280\nhttps://logging.apache.org/security.html#CVE-2026-40021\nhttps://logging.apache.org/cyclonedx/vdr.xml\nhttps://logging.apache.org/log4net/manual/configuration/layouts.html\nhttps://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7\n","enisa_id":"EUVD-2026-21488\n","assigner":"apache","epss":0.77,"dataProcessed":"Oct 27, 2026, 7:16:42 AM","vulnerabilityProduct":[{"id":"14108bd9-41b4-3f05-bbd1-399127a5dddd","product":{"name":"Apache log4net","vendor":{"name":"Apache Software Foundation"}},"product_version":"0 \u003c3.3.0"}],"vulnerabilityVendor":[{"id":"ed32f043-3d1e-3c19-bc3c-09632798ef36","vendor":{"name":"Apache Software Foundation"}}]}}],"enisaIdAdvisory":[{"id":"bd6815d1-4810-3c58-87a0-ffe2b3433113","advisory":{"id":"WID-SEC-W-2026-1054","description":"Apache log4net: Schwachstelle ermöglicht Manipulation von Dateien","summary":"Ein entfernter, anonymer Angreifer kann eine Schwachstelle in Apache log4net ausnutzen, um Dateien zu manipulieren.","datePublished":"Apr 12, 2026, 10:00:00 PM","dateUpdated":"Apr 14, 2026, 10:00:00 PM","baseScore":0.0,"references":"https://wid.cert-bund.de/.well-known/csaf/white/2026/wid-sec-w-2026-1054.json\nhttps://wid.cert-bund.de/portal/wid/securityadvisory?name\u003dWID-SEC-2026-1054\n","aliases":"CVE-2026-40021\n","source":{"id":8,"name":"csaf_certbund"},"advisoryProduct":[{"id":"9a57c7b1-8417-3825-b4c7-5d739cf0488e","product":{"name":"log4net","vendor":{"name":"Apache"}}},{"id":"c8707e05-a66f-31a6-b802-e6721807fc0f","product":{"name":"3.3.0","vendor":{"name":"Apache"}}}]}}]}