CVE-2026-105243
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.
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
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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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
| Package | Affected | Fixed |
|---|---|---|
log4netDebian:13 |
All versions, plus listed versions 1.2.10+dfsg-101.2.10+dfsg-9 |
None known |
log4netDebian:14 |
All versions, plus listed versions 1.2.10+dfsg-101.2.10+dfsg-9 |
None known |
log4netUbuntu: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 |
log4netUbuntu:18.04:LTS |
All versions, plus listed versions 1.2.10+dfsg-71.2.10+dfsg-7ubuntu0.18.04.1 |
None known |
log4netUbuntu:20.04:LTS |
All versions, plus listed versions 1.2.10+dfsg-71.2.10+dfsg-7ubuntu0.20.04.1 |
None known |
log4netUbuntu:22.04:LTS |
All versions, plus listed versions 1.2.10+dfsg-8 |
None known |
log4netUbuntu:24.04:LTS |
All versions, plus listed versions 1.2.10+dfsg-81.2.10+dfsg-9 |
None known |
log4netUbuntu:26.10 |
All versions, plus listed versions 1.2.10+dfsg-9build11.2.10+dfsg-10 |
None known |
log4netUbuntu:26.04:LTS |
All versions, plus listed versions 1.2.10+dfsg-91.2.10+dfsg-9build1 |
None known |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE 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
github.com/apache/logging-log4net/pull/315
github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed
lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp
openwall.com/lists/oss-security/2026/10/07/17
nvd.nist.gov/vuln/detail/CVE-2026-105243
github.com/advisories/GHSA-j8mm-w573-8v6c
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nuget.org/packages
github.com/CVEProject/cvelistV5/tree/main/cves/2026/105xxx/CVE-2026-105243.json
gitbox.apache.org/repos/asf/logging-log4net.git
security-tracker.debian.org/tracker/CVE-2026-105243
ubuntu.com/security/CVE-2026-105243
cve.org/CVERecord?id=CVE-2026-105243
lists.apache.org/thread/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp