CVE Explorer
CVE-2026-40021
Apache Log4net's 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
Known exploited
Not asserted
Disputed
No
Stale source
No
Conflicts
0
Affected products and versions
1 source assertion{"collectionURL":"https://www.nuget.org/packages","cpes":["cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*"],"defaultStatus":"unaffected","packageName":"log4net","packageURL":"pkg:nuget/log4net","product":"Apache Log4net","vendor":"Apache Software Foundation","versions":[{"lessThan":"3.3.0","status":"affected","version":"0","versionType":"nuget"}]}
- cve_program_cvelist_v5affectedurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/affected/0
Provider-owned CVSS observations
1 source assertion{"metric":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"HIGH","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":6.3,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"LOW","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"N…
- cve_program_cvelist_v5cvssurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/metrics/0/cvssV4_0
CWE assertions
1 source assertion{"cweId":"CWE-116","description":"CWE-116 Improper Encoding or Escaping of Output","lang":"en","type":"CWE"}
- cve_program_cvelist_v5cweurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/problemTypes/0/descriptions/0
Source references
6 source assertions{"url":"http://www.openwall.com/lists/oss-security/2026/04/10/11"}
- cve_program_cvelist_v5referenceurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/adp/0/references/0
{"tags":["patch"],"url":"https://github.com/apache/logging-log4net/pull/280"}
- cve_program_cvelist_v5referenceurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/references/0
{"tags":["vendor-advisory"],"url":"https://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7"}
- cve_program_cvelist_v5referenceurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/references/4
{"tags":["vendor-advisory"],"url":"https://logging.apache.org/cyclonedx/vdr.xml"}
- cve_program_cvelist_v5referenceurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/references/2
{"tags":["related"],"url":"https://logging.apache.org/log4net/manual/configuration/layouts.html"}
- cve_program_cvelist_v5referenceurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/references/3
{"tags":["vendor-advisory"],"url":"https://logging.apache.org/security.html#CVE-2026-40021"}
- cve_program_cvelist_v5referenceurn:baitaphish:normalized-source-record:v2:eaf510dfe68842ef87fb6c5dc8d7b1bbb90f2716de77f36074b46c0d524323f8 · sha256:716815ee01cf1e04… · /containers/cna/references/1
Attribution and limitations
- CVE Program CVEList V5: Reproduce the MITRE copyright designation and CVE license in copies. Source →
Provider severity values are preserved separately. Baitaphish does not convert them into a risk rating, infer affected products, or treat EPSS as observed exploitation.