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  4. CVE 2026 105239 apache log4net nul character truncates
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Back to active CVEs
Medium · CVSS 5.3CVE-2026-105239

Apache log4net: NUL character truncates EventLogAppender recordsCVE-2026-105239

Answer in brief

CVE-2026-105239 records a Medium severity (CVSS 5.3) vulnerability in Apache log4net: NUL character truncates EventLogAppender records. The current sources do not mark it as known exploited. The current feed maps Apache Software Foundation/log4net (generic), Apache Software Foundation/log4net (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 6, 2026Updated Oct 6, 2026Source checked Oct 7, 2026First seen by HOL Oct 6, 2026Material review Oct 6, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 5.3
Exploitation
Not marked as known exploited
Affected software
2 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 5.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Apache Software Foundation/log4net (generic), Apache Software Foundation/log4net (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
Apache Software Foundation/log4netgeneric>=1.2.9 <3.5.03.5.0
Apache Software Foundation/log4netgeneric>=02e1e115435888485f2e28b414d267e39e799e07 <dc5855a0720c91590fd7a81d729ea01fdd69e000dc5855a0720c91590fd7a81d729ea01fdd69e000

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for Apache Software Foundation/log4net, Apache Software Foundation/log4net.
  2. 2Review the reported fix. Update Apache Software Foundation/log4net to 3.5.0; Apache Software Foundation/log4net to dc5855a0720c91590fd7a81d729ea01fdd69e000 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

  1. Published upstream

    Oct 6, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Oct 6, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Oct 6, 2026

Sources and claim methodology

  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • Source referencelists.apache.org
Upstream source 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.

Quoted source text, attributed separately from HOL analysis.

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  • Langflow OSS is affected by multiple vulnerabilitiesSame generic ecosystem
  • Langflow OSS is affected by multiple vulnerabilitiesSame generic ecosystem

Record context

Vulnerability class
Vulnerability
EPSS
Not reported
CWE IDs
CWE-158
Source
CVE List V5
Source checked
Oct 7, 2026
References
3 linked sources
Open source record