CVE-2026-105241
Improper Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.
Does this matter?
Lower severity and a low EPSS score (0.82%). Track it; it rarely justifies an emergency change on its own.
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.
- 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
- 0.82% probability · 57th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-176
- 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/4d2e10f0908199604b4326f9df6d0b43b871e333Patch
- https://github.com/apache/logging-log4net/pull/315Patch
- https://lists.apache.org/thread.html/hg8dgh3oy8bp3dhb8nsygk9kw2o401wsMailing List, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/10/07/15Mailing 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.