CVE-2026-105240
Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender 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
Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net. A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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-158
- 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/6046fe9d7f353b49fe995361c071ec2eea8f7ef6Patch
- https://github.com/apache/logging-log4net/pull/315Patch
- https://lists.apache.org/thread.html/gyw2d4ppy82t1vlpdknkfd1nmzp21z17Mailing List, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/10/07/18Mailing 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.