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CVE-2026-105239— Apache log4net: NUL character truncates EventLogAppender records

Quick assessment

Affected
Apache Software Foundation Apache log4net
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Apache log4net 的 EventLogAppender 中存在“对空字节（NUL 字符）的处理不当”漏洞。 当日志内容中包含 NUL 字符时，Windows 事件日志记录会在该位置被截断，导致布局渲染器在此之后生成的所有内容（包括异常文本和尾部字段）均被静默丢弃、未存储。攻击者若能将数据注入到日志消息中，即可隐藏该记录后续的部分内容。此漏洞仅影响在 Windows 平台上使用 EventLogAppender 的应用程序。 受影响版本为 Apache log4net 1.2.9 至 3.5.0（不含 3

CVSS 5.3 · Medium

Affected Version Matrix 2

VendorProduct Version RangeStatus
Apache Software Foundation Apache log4net 1.2.9< 3.5.0 affected
02e1e115435888485f2e28b414d267e39e799e07< dc5855a0720c91590fd7a81d729ea01fdd69e000 affected
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I. Basic Information for CVE-2026-105239

Vulnerability Information
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Vulnerability Title
Apache log4net: NUL character truncates EventLogAppender records
Source: CVE Program / CVE List V5
Vulnerability Description
Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net. A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use EventLogAppender 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
空字节或NULL字符转义处理不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Apache Software Foundation Apache log4net 1.2.9 ~ 3.5.0 -
Apache Software Foundation Apache log4net 02e1e115435888485f2e28b414d267e39e799e07 ~ dc5855a0720c91590fd7a81d729ea01fdd69e000 -

II. Public POCs for CVE-2026-105239

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III. Intelligence Information for CVE-2026-105239

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Other References for CVE-2026-105239 (3)

Same Patch Batch · Apache Software Foundation · 2026-10-06 · 8 CVEs total

CVE-2026-94114 5.9 MEDIUM Apache Commons BCEL: Nested Code/Record attributes drive unbounded parse-time recursion in
CVE-2026-105244 5.3 MEDIUM Apache log4net: RemoteSyslogAppender silently deletes non-ASCII content
CVE-2026-105243 5.3 MEDIUM Apache log4net: Oversize EventLogAppender record silently discarded
CVE-2026-105242 5.3 MEDIUM Apache log4net: Request validation failure drops the event in the aspnet-request converter
CVE-2026-105241 5.3 MEDIUM Apache log4net: Unencodable content discards a whole SmtpPickupDirAppender batch
CVE-2026-105240 5.3 MEDIUM Apache log4net: NUL character truncates OutputDebugStringAppender records
CVE-2026-105111 4.7 MEDIUM Apache Commons BCEL: Class2HTML emits unescaped class strings, enabling stored XSS

IV. Related Vulnerabilities

Same product: Apache log4net
Same vendor: Apache Software Foundation
Same weakness: CWE-158

V. Comments for CVE-2026-105239

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