5.3

CVE-2026-105241: apache software foundation apache log4net Improper Handling of Unicode Encoding

CVSS: 5.3v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-105241DEBIAN-CVE-2026-105241
Published 06-10-2026Last modified 07-10-2026
Open JSON

Vulnerability summary

CVE-2026-105241 is a medium (CVSS 5.3) Improper Handling of Unicode Encoding vulnerability in apache software foundation apache log4net. EPSS estimates a 0.82% chance of exploitation in the next 30 days, higher than 56.5% 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
0.82%
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 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 metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.82%

Chance of exploitation in the next 30 days

Percentile

57%

Versus all other CVEs

30-day change

Change unavailable

Change unavailable

07-10-202618-10-2026
EPSS score
0.82%

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, < 4d2e10f0908199604b4326f9df6d0b43b871e333
Debian1 product
  • log4netAll versions (No fix recorded)
Ubuntu1 product
  • log4netAll versions (No fix recorded)

4 vendors · 4 products

References

8 links