CVE-2026-40021
unknown
CVSS v3
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CVSS v4 NEW
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VIR risk
—
Description
Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters
Predictions
Exploit likelihood
30%
Patch ETA
—
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| sles | affected | | |
| debian | bullseye | affected | |
| debian | sid | affected | |
| debian | trixie | affected | |
Package impact
| Ecosystem | Package | Vulnerable | Fixed |
|---|---|---|---|
| NuGet | log4net | <3.3.0 | 3.3.0 |
References
- https://www.suse.com/security/cve/CVE-2026-40021.html
- https://security-tracker.debian.org/tracker/CVE-2026-40021
- https://nvd.nist.gov/vuln/detail/CVE-2026-40021
- https://github.com/apache/logging-log4net/pull/280
- https://github.com/apache/logging-log4net
- https://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7
- https://logging.apache.org/cyclonedx/vdr.xml
- https://logging.apache.org/log4net/manual/configuration/layouts.html
- https://logging.apache.org/security.html#CVE-2026-40021
- http://www.openwall.com/lists/oss-security/2026/04/10/11
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.