An attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.
Users are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.
Metrics
Affected Vendors & Products
No advisories yet.
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
Fri, 10 Apr 2026 18:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
|
Fri, 10 Apr 2026 17:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
Fri, 10 Apr 2026 16:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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 and the silent loss of the affected log event. An attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity. Users are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue. | |
| Title | Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters | |
| First Time appeared |
Apache
Apache log4net |
|
| Weaknesses | CWE-116 | |
| CPEs | cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Apache
Apache log4net |
|
| References |
| |
| Metrics |
cvssV4_0
|
Projects
Sign in to view the affected projects.
Status: PUBLISHED
Assigner: apache
Published:
Updated: 2026-04-10T17:35:01.228Z
Reserved: 2026-04-08T10:03:43.840Z
Link: CVE-2026-40021
Updated: 2026-04-10T16:18:21.980Z
Status : Received
Published: 2026-04-10T16:16:32.420
Modified: 2026-04-10T17:17:12.030
Link: CVE-2026-40021
No data.
OpenCVE Enrichment
No data.