Create Hotfix Version for Communication Studio – Update log4net to 3.3.1

A new Hotfix (HF) version needs to be created for Communication Studio to address security vulnerabilities caused by the currently used log4net dependency.

The application is currently using log4net version < 3.3.0, which contains known vulnerabilities identified during dependency/security scans.

To mitigate these issues, the dependency should be upgraded to log4net version 3.3.1.

The update must be validated to ensure compatibility with the existing logging implementation and configurations.

Impact Assessment

Impact: Low (Environment-Specific Risk)

The identified vulnerability CVE-2026-40021 / GHSA-4f7c-pmjv-c25w affects log4net versions prior to 3.3.0 and is related to silent log event loss in XmlLayout and XmlLayoutSchemaLog4J when invalid XML characters are processed. (GitHub)

Based on the current assessment, the issue primarily impacts logging integrity and audit trail reliability rather than core system security. There is currently no indication that the vulnerability enables:

• remote code execution,

• privilege escalation,

• authentication bypass,

• or unauthorized data access. (GitHub)

The potential impact is limited to silently dropped log entries in specific XML logging scenarios involving attacker-influenced input. (GitHub)

For the current CommunicationStudio deployment, the operational risk is considered low because:

• the application is an internal desktop application,

• access is restricted to authorized users,

• and there is no public exposure.

At present, no practical exploit path leading to system compromise has been identified in the current deployment context.

Further technical verification is required to confirm whether vulnerable XML layouts are actively used and whether externally controlled input can affect logging behavior.

Although the official CVE severity is classified as Medium, the environment-specific operational risk for the current deployment is currently assessed as Low.

References

• https://www.nuget.org/packages/log4net 
• https://github.com/advisories/GHSA-4f7c-pmjv-c25w