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TI-2026-68921 Aliases CVE-2026-105241GHSA-r5vq-477m-wcfc

Unencodable content drops a whole batch in Apache log4net appender

Priority LOW 32CWE-176Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
None · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA.

Summary

Apache log4net from 1.2.9 before 3.5.0 has an improper handling of Unicode encoding flaw (CWE-176) in SmtpPickupDirAppender. Content that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, makes the write throw and discards every buffered event in the batch. An unauthenticated remote attacker whose data reaches a log message can suppress the records of other events, and a truncated mail may be left in the pickup directory. Only applications that use SmtpPickupDirAppender are affected.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00824 57th percentileScored 2026-11-07
Fix Fixed Apache log4net (Apache Software Foundation): 3.5.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
ApacheApache log4net1.2.9 to before 3.5.03.5.0Patch availableCNA
  • Apache log4net VendorApache Affected 1.2.9 to before 3.5.0 Fixed in 3.5.0 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*1.2.9 to before 3.5.0VulnerableApache
  • cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:* Versions 1.2.9 to before 3.5.0 Vulnerable ·Apache

Remediation

Upgrade Apache log4net to version 3.5.0, which fixes the issue.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

  • Fix · CNA Apache log4net (Apache Software Foundation) Fixed in 3.5.0

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    Apache log4net 3.5.0

    6 records Highest priority Priority LOW 6 LOW

    Other records, highest priority first

    • TI-2026-68924 RemoteSyslogAppender in Apache log4net silently drops non-ASCII textPriority LOW 32
    • TI-2026-68923 Apache log4net EventLogAppender silently discards oversize recordsPriority LOW 32
    • TI-2026-68922 Log4net drops log events when ASP.NET request validation failsPriority LOW 32
    Show all 6 records →

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-06 Threatist record created from CVE-2026-105241
  2. 2026-10-07 Alias added: GHSA-r5vq-477m-wcfc
  3. 2026-10-07 CISA SSVC decision points changed
  4. 2026-10-07 Affected versions changed · Red Hat
  5. 2026-10-07 CVSS score added · Red Hat
  6. 2026-10-11 EPSS moved to the 50th–90th percentile

References

Patch 2

Advisory 2

  • TI-2018-01190 XML external entity injection in Apache log4net CVSS 3.1CRITICAL 9.8
  • TI-2026-68924 RemoteSyslogAppender in Apache log4net silently drops non-ASCII text CVSS 3.1MEDIUM 5.3
  • TI-2026-68923 Apache log4net EventLogAppender silently discards oversize records CVSS 3.1MEDIUM 5.3
  • TI-2026-68922 Log4net drops log events when ASP.NET request validation fails CVSS 3.1MEDIUM 5.3
  • TI-2026-68920 NUL character truncates log records in Apache log4net debug output CVSS 3.1MEDIUM 5.3
  • TI-2026-68919 NUL character truncates EventLogAppender records in Apache log4net CVSS 3.1MEDIUM 5.3
See all 8 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences