Description
Apache Log4cxx's XMLLayout https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html , in versions before 1.7.0, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in log messages, NDC, and MDC property keys and values, producing invalid XML output. Conforming XML parsers must reject such documents with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.
An attacker who can influence logged data can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.
Users are advised to upgrade to Apache Log4cxx 1.7.0, which fixes this issue.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Apache Software Foundation | Apache Log4cxx | < 1.7.0 | 1.7.0 |
| Apache Software Foundation | Apache Log4cxx (Conan) | < 1.7.0 | 1.7.0 |
| Apache Software Foundation | Apache Log4cxx (Brew) | < 1.7.0 | 1.7.0 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | log4cxx | No fix yet | — |
| Debian 13 | log4cxx | No fix yet | — |
| Debian 12 | log4cxx | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | log4cxx | No fix yet | — |
| Ubuntu 26.04 LTS | log4cxx | No fix yet | — |
| Ubuntu 25.10 | log4cxx | No fix yet | — |
| Ubuntu 24.04 LTS | log4cxx | No fix yet | — |
| Ubuntu 22.04 LTS | log4cxx | No fix yet | — |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | log4cxx | No fix yet | — |
| Ubuntu 18.04 LTS | log4cxx | No fix yet | — |
| Ubuntu 16.04 LTS | log4cxx | No fix yet | — |
| Ubuntu 14.04 LTS | log4cxx | No fix yet | — |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | log4cxx | 1.7.0-2.1 | openSUSE-SU-2026:10566-1 |
Advisories 2
- WID-SEC-2026-2292 Apache log4j und Log4cxx: Mehrere Schwachstellen ermöglichen Manipulation von Dateien BSI CERT-Bund (WID) · Nov 1, 2026
- openSUSE-SU-2026:10566-1 liblog4cxx-devel-1.7.0-2.1 on GA media SUSE / openSUSE Security Updates · Apr 17, 2026
References
- https://github.com/apache/logging-log4cxx/pull/609 patch
- https://logging.apache.org/security.html#CVE-2026-40023 vendor-advisory
- https://logging.apache.org/cyclonedx/vdr.xml vendor-advisory
- https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html related
- https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b vendor-advisory