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CVE-2026-105244

Apache log4net: RemoteSyslogAppender silently deletes non-ASCII content

5.3 Medium

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
Low
Availability
None

Exploit likelihood

0.82%Up 0.5 points since Oct 7, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.3

Apache log4net: RemoteSyslogAppender silently deletes non-ASCII content

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Record
CVE-2026-105244
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-116
Updated
2026-11-02
EUVDEUVD-2026-93870 5.3

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Record
EUVD-2026-93870
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-g956-ph29-3vq5 5.3

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache...

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Record
GHSA-g956-ph29-3vq5
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-116
Updated
2026-11-02
NVD 5.3

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Record
CVE-2026-105244
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-116
Updated
2026-11-02
OSV 5.3

Apache log4net: RemoteSyslogAppender silently deletes non-ASCII content

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Record
CVE-2026-105244
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-116
Updated
2026-11-02
OSVDEBIAN-CVE-2026-105244 5.3

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net. Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected. This issue affects Apache log4net: from 1.2.12 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Record
DEBIAN-CVE-2026-105244
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-105244 5.3

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net. Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected. This issue affects Apache log4net: from 1.2.12 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Record
UBUNTU-CVE-2026-105244
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
log4net
Debian:13
All versions, plus listed versions
1.2.10+dfsg-101.2.10+dfsg-9
None known
log4net
Debian:14
All versions, plus listed versions
1.2.10+dfsg-101.2.10+dfsg-9
None known
log4net
Ubuntu:16.04:LTS
All versions, plus listed versions
1.2.10+dfsg-61.2.10+dfsg-71.2.10+dfsg-7ubuntu0.16.04.1
None known
log4net
Ubuntu:18.04:LTS
All versions, plus listed versions
1.2.10+dfsg-71.2.10+dfsg-7ubuntu0.18.04.1
None known
log4net
Ubuntu:20.04:LTS
All versions, plus listed versions
1.2.10+dfsg-71.2.10+dfsg-7ubuntu0.20.04.1
None known
log4net
Ubuntu:22.04:LTS
All versions, plus listed versions
1.2.10+dfsg-8
None known
log4net
Ubuntu:24.04:LTS
All versions, plus listed versions
1.2.10+dfsg-81.2.10+dfsg-9
None known
log4net
Ubuntu:26.10
All versions, plus listed versions
1.2.10+dfsg-9build11.2.10+dfsg-10
None known
log4net
Ubuntu:26.04:LTS
All versions, plus listed versions
1.2.10+dfsg-91.2.10+dfsg-9build1
None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-105244 is a medium vulnerability (CVSS 5.3) in Apache Log4net, published October 6, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.82%, the 57th percentile. No source names a fixed version.

References

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