CVE-2026-105239: medium-severity vulnerability in Apache log4net
Apache log4net: NUL character truncates EventLogAppender records
Published · Updated
13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 5.3epss 0.3%
exploitation probability
0.3%top 75% of all CVEs
observed exploitation
nono source reports it
Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net.
A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. 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/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Affected products
Apache Software Foundation · Apache log4netRelated CVEs — Apache log4net
In the same product, most dangerous first.
CVE-2026-105244MEDIUMApache log4net: RemoteSyslogAppender silently deletes non-ASCII contentEPSS 0.3%CVE-2026-105242MEDIUMApache log4net: Request validation failure drops the event in the aspnet-request converterEPSS 0.3%CVE-2026-105241MEDIUMApache log4net: Unencodable content discards a whole SmtpPickupDirAppender batchEPSS 0.3%CVE-2026-105243MEDIUMApache log4net: Oversize EventLogAppender record silently discardedEPSS 0.3%CVE-2026-105240MEDIUMApache log4net: NUL character truncates OutputDebugStringAppender recordsEPSS 0.3%