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CVE-2026-105243

Apache log4net: Oversize EventLogAppender record silently discarded

5.3 Medium

Insufficient 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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
Low
Availability
None

Exploit likelihood

0.81%Up 0.5 points since Oct 7, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.3

Apache log4net: Oversize EventLogAppender record silently discarded

Insufficient 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.

Record
CVE-2026-105243
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-778
Updated
2026-11-02
EUVDEUVD-2026-93869 5.3

Insufficient 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.

Record
EUVD-2026-93869
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-j8mm-w573-8v6c 5.3

Insufficient Logging vulnerability in the EventLogAppender of Apache log4net. Long messages were...

Insufficient 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.

Record
GHSA-j8mm-w573-8v6c
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-778
Updated
2026-11-02
NVD 5.3

Insufficient 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.

Record
CVE-2026-105243
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-778
Updated
2026-11-02
OSV 5.3

Apache log4net: Oversize EventLogAppender record silently discarded

Insufficient 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.

Record
CVE-2026-105243
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-778
Updated
2026-11-02
OSVDEBIAN-CVE-2026-105243 5.3

Insufficient 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.

Record
DEBIAN-CVE-2026-105243
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-105243 5.3

Insufficient 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.

Record
UBUNTU-CVE-2026-105243
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
log4net
Debian:13
All versions, plus listed versions
1.2.10+dfsg-101.2.10+dfsg-9
None known
log4net
Debian:14
All versions, plus listed versions
1.2.10+dfsg-101.2.10+dfsg-9
None known
log4net
Ubuntu:16.04:LTS
All versions, plus listed versions
1.2.10+dfsg-61.2.10+dfsg-71.2.10+dfsg-7ubuntu0.16.04.1
None known
log4net
Ubuntu:18.04:LTS
All versions, plus listed versions
1.2.10+dfsg-71.2.10+dfsg-7ubuntu0.18.04.1
None known
log4net
Ubuntu:20.04:LTS
All versions, plus listed versions
1.2.10+dfsg-71.2.10+dfsg-7ubuntu0.20.04.1
None known
log4net
Ubuntu:22.04:LTS
All versions, plus listed versions
1.2.10+dfsg-8
None known
log4net
Ubuntu:24.04:LTS
All versions, plus listed versions
1.2.10+dfsg-81.2.10+dfsg-9
None known
log4net
Ubuntu:26.10
All versions, plus listed versions
1.2.10+dfsg-9build11.2.10+dfsg-10
None known
log4net
Ubuntu:26.04:LTS
All versions, plus listed versions
1.2.10+dfsg-91.2.10+dfsg-9build1
None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-105243 is a medium vulnerability (CVSS 5.3) in Apache Log4net, published October 6, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.81%, the 57th percentile. No source names a fixed version.

References

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