CVE-2026-105241: medium-severity vulnerability in Apache log4net
Apache log4net: Unencodable content discards a whole SmtpPickupDirAppender batch
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 Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.
Content that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, made the write throw. Every buffered event in the batch was discarded, not only the one carrying the content, and a truncated mail could be left in the pickup directory. A party whose data reaches a log message could suppress the records of other events. Only applications that use SmtpPickupDirAppender 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-2026-105239MEDIUMApache log4net: NUL character truncates EventLogAppender recordsEPSS 0.3%CVE-2026-105243MEDIUMApache log4net: Oversize EventLogAppender record silently discardedEPSS 0.3%CVE-2026-105240MEDIUMApache log4net: NUL character truncates OutputDebugStringAppender recordsEPSS 0.3%