# Apache log4net: NUL character truncates EventLogAppender records

CVE record · `CVE-2026-105239`

- **Identifiers:** `CVE-2026-105239`
- **State:** Confirmed
- **Severity:** CVSS 5.3 Medium
- **Critical:** No
- **CNA:** apache
- **Weakness (CWE):** [CWE-158](https://cwe.mitre.org/data/definitions/158.html)
- **Tags:** [CWE-158](https://agentprime.io/advisories/tag/cwe-158.md)
- **Technologies:** [Apache Software Foundation Apache log4net](https://agentprime.io/advisories/technology/apache-software-foundation-apache-log4net.md)
- **Published:** 6 Oct 2026
- **Updated:** 7 Oct 2026
- **Reviewed by a person:** No

Published by the CVE Program (CNA: apache) at 6 Oct 2026, 19:46 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

## Affected products, as the CNA wrote them

- Vendor: Apache Software Foundation. Product: Apache log4net.
  - affected: `1.2.9 to before 3.5.0` (semver)
  - Other versions: unaffected
  - Package name: `log4net`
  - Collection: `https://nuget.org/packages`
  - purl: `pkg:nuget/log4net`
- Vendor: Apache Software Foundation. Product: Apache log4net.
  - affected: `02e1e115435888485f2e28b414d267e39e799e07 to before dc5855a0720c91590fd7a81d729ea01fdd69e000` (git)
  - Other versions: unaffected
  - Package name: `log4net`
  - Collection: `https://nuget.org/packages`
  - purl: `pkg:nuget/log4net`

## Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

## Severity and exploitation

- 5.3 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`, from CNA (apache)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0082, the 57th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the CVE Program, published 6 Oct 2026. New records show when each source confirmed them.

## Sources

- [CVE List: CVE-2026-105239](https://www.cve.org/CVERecord?id=CVE-2026-105239)
- [NVD: CVE-2026-105239](https://nvd.nist.gov/vuln/detail/CVE-2026-105239)

### References from the CNA

- <https://github.com/apache/logging-log4net/pull/315> (patch)
- <https://github.com/apache/logging-log4net/commit/dc5855a0720c91590fd7a81d729ea01fdd69e000> (patch)
- <https://lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq> (vendor-advisory)

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.

## Check whether this affects you

This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it. Compare the affected versions above with what you run.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), `get_advisory` returns this record and `search_advisories` finds related ones. Setup: <https://agentprime.io/mcp.md>
- As JSON: <https://api.agentprime.io/v1/advisories/CVE-2026-105239>
- Everything that needs attention now: <https://agentprime.io/advisories/critical.md>

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The web page: <https://agentprime.io/advisories/CVE-2026-105239/>. Everything for agents: <https://agentprime.io/llms.txt>.