Apache log4net: Oversize EventLogAppender record silently discarded

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-105243
StatePUBLISHED
Assignerapache
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-06 20:17:16 UTC
Updated2026-10-09 15:26:03 UTC
DescriptionInsufficient Logging vulnerability in the EventLogAppender of Apache log4net. Long messages were truncated to a fixed size that exceeds what the Windows Event Log accepts once the log and source names are counted, and the event log then stored nothing and reported nothing. A party whose data reaches a log message could suppress the whole record by making it long enough. Only applications on Windows that use EventLogAppender are affected. This issue affects Apache log4net: from 1.2.9 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS: 0.008060000 probability, percentile 0.556090000 (date 2026-10-11)

Problem Types: CWE-778 | CWE-778 CWE-778 Insufficient Logging

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
3.1CNACVSS5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Apache Log4net All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Apache Software Foundation Apache Log4net affected 1.2.9 3.5.0 semver Not specified
CNA Apache Software Foundation Apache Log4net affected 02e1e115435888485f2e28b414d267e39e799e07 28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed git Not specified

References

ReferenceSourceLinkTags
lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp [email protected] lists.apache.org Mailing List, Vendor Advisory
github.com/apache/logging-log4net/pull/315 [email protected] github.com Patch
www.openwall.com/lists/oss-security/2026/10/07/17 af854a3a-2127-422b-91ae-364da2661108 www.openwall.com Mailing List, Third Party Advisory
github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dd... [email protected] github.com Patch
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: The Apache Software Foundation (en)

CNA: Claude Security (en)

CNA: Jan Friedrich (en)

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