CVE-2026-40021: Apache Log4net's XmlLayout and
This Apache advisory covers CVE-2026-40021 in Apache Log4net.
- CVE-2026-40021
Key facts
- Vendor rating
- Medium, CVSS 6.3
- CISA KEV
- Not listed (catalogue checked )
- Affected
- 3.3.0
- Fixed in
- 3.3.0
- Source published
- Source revised
- Listed by VulniPulse
Compiled by VulniPulse from the linked sources. How records are collected and checked.
Affected products & platforms
Description
Apache Log4net's XmlLayout and XmlLayoutSchemaLog4J, in versions before 3.3.0, fail to sanitize characters forbidden by the XML 1.0 specification 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.
Text from the source record.
How to fix CVE-2026-40021
Upgrade to a fixed release named by Apache:
- 3.3.0
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