November 4, 2026

CVE Watchtower

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CVE-2026-40021NVD

Vulnerability Summary

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.
Severity Level
MEDIUM
Published Date
Apr 10, 2026
Last Modified
Apr 14, 2026
Exploitation Status
No confirmed exploitation yet
CVE Record Status
Published
EPSS Score (30-Day)
0.29%Probability
Root Weakness (CWE)
CWE-116: Unknown/Unlisted Weakness ↗
Refer to the official MITRE database for detailed architectural specifications regarding this weakness.
CVSS v4.0 Base Metrics — Score 6.3
Attack VectorNetwork
Attack ComplexityHigh
Attack RequirementsNone
Privileges RequiredNone
User InteractionNone
Confidentiality (Vulnerable System)None
Integrity (Vulnerable System)None
Availability (Vulnerable System)None
Confidentiality (Subsequent System)None
Integrity (Subsequent System)Low
Availability (Subsequent System)None

Affected & Patched Versions

Affected Versions
  • log4net < 3.3.0
Patched Versions
Not provided by Private for this CVE.
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🎁7-Day Free Trial — Try Pro or Team, no card required.
📧Email Delivery — Threat intel straight to your inbox.
♾️Unlimited Vendors — Track your entire stack.
🚨All New CVEs — Be the first to know.
📈EPSS Spike Alerts — Catch rising risk before it peaks.
🎯Custom EPSS/CVSS — Filter noise, focus on risk.
🛡️Exploit Intel — A 2nd confirmed-exploit signal beyond KEV.
🐙GitHub Issues — Auto-tracked, no duplicates.
📬Weekly Digest — One clean summary, not inbox spam.
🏷️Watchlist Groups — Tag alerts by team (Infra/AppSec/SOC).
💬Webhooks — Slack & Teams integration.
🔀Smart Routing — Critical alerts to one channel, rest to another.
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External References