CVE-2026-105243
Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.
Does this matter?
Lower severity and a low EPSS score (0.81%). Track it; it rarely justifies an emergency change on its own.
Description
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.
- CVSS 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- EPSS
- 0.81% probability · 57th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-778
- Affected
- apache/log4net
- Source
- security@apache.org
EPSS moved from 0.3% on 7 October 2026 to 0.8% on 26 October 2026.
References
- https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffedPatch
- https://github.com/apache/logging-log4net/pull/315Patch
- https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rpMailing List, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/10/07/17Mailing List, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.