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CVE-2026-105240

Apache log4net: NUL character truncates OutputDebugStringAppender records

5.3 Medium

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

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

0.81%Up 0.5 points since Oct 7, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.3

Apache log4net: NUL character truncates OutputDebugStringAppender records

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

Record
CVE-2026-105240
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-158
Updated
2026-11-02
EUVDEUVD-2026-93864 5.3

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

Record
EUVD-2026-93864
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-q2xj-998m-58gf 5.3

Improper Neutralization of Null Byte or NUL Character vulnerability in the...

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

Record
GHSA-q2xj-998m-58gf
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-158
Updated
2026-11-02
NVD 5.3

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

Record
CVE-2026-105240
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-158
Updated
2026-11-02
OSV 5.3

Apache log4net: NUL character truncates OutputDebugStringAppender records

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

Record
CVE-2026-105240
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-158
Updated
2026-11-02
OSVDEBIAN-CVE-2026-105240 5.3

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net. A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

Record
DEBIAN-CVE-2026-105240
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-2026-105240 5.3

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net. A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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.

Record
UBUNTU-CVE-2026-105240
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-2026-105240 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 0.81%, the 57th percentile. No source names a fixed version.

References

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