CVE-2026-105241

Name	CVE-2026-105241
Description	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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
log4net (PTS)	trixie	1.2.10+dfsg-9	vulnerable
	forky, sid	1.2.10+dfsg-10	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
log4net	source	(unstable)	(unfixed)

Notes

https://github.com/apache/logging-log4net/pull/315
Fixed by: https://github.com/apache/logging-log4net/commit/4d2e10f0908199604b4326f9df6d0b43b871e333 (rc/3.5.0-rc1)
https://lists.apache.org/thread/hg8dgh3oy8bp3dhb8nsygk9kw2o401ws