5.3

CVE-2026-105240: apache software foundation apache log4net

CVSS: 5.3v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-105240DEBIAN-CVE-2026-105240
Published 06-10-2026Last modified 07-10-2026
Open JSON

Vulnerability summary

CVE-2026-105240 is a medium (CVSS 5.3) vulnerability in apache software foundation apache log4net. EPSS estimates a 0.81% chance of exploitation in the next 30 days, higher than 56% of scored vulnerabilities.

Overall risk
21/100
0100
Low · default modelHow is this calculated?
CVSS score
5.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.81%
0%100%
Low · Change unavailable
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 06-10-2026
    PublishedVulnerability first disclosed.
  2. 07-10-2026
    Last modifiedVulnerability information updated.

Description

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.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.81%

Chance of exploitation in the next 30 days

Percentile

56%

Versus all other CVEs

30-day change

Change unavailable

Change unavailable

07-10-202618-10-2026
EPSS score
0.81%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Apache1 product
Apache software foundation1 product
  • apache log4net≥ 1.2.9, < 3.5.0 | ≥ 02e1e115435888485f2e28b414d267e39e799e07, < 6046fe9d7f353b49fe995361c071ec2eea8f7ef6
Debian1 product
  • log4netAll versions (No fix recorded)
Ubuntu1 product
  • log4netAll versions (No fix recorded)

4 vendors · 4 products

References

8 links