CVE-2025-59940 is a medium-severity vulnerability identified in the mondeja mkdocs-include-markdown-plugin, a plugin used with Mkdocs to include Markdown content from external files. The vulnerability exists in versions 7.1.7 and below and is classified under CWE-20, which relates to improper input validation. Specifically, the plugin fails to properly validate input that can collide with substitution placeholders during Markdown content inclusion. This improper input validation can lead to unintended substitution behavior, potentially allowing an attacker to manipulate the content processing pipeline. The CVSS v3.1 base score is 6.5, reflecting a network exploitable vulnerability with low attack complexity, no privileges required, and no user interaction needed. The impact vector indicates that while confidentiality is not affected, the integrity and availability of the Markdown rendering process can be compromised. This could result in altered or corrupted documentation outputs or denial of service conditions in systems relying on automated documentation generation. The issue was fixed in version 7.1.8 of the plugin. There are no known exploits in the wild as of the publication date, and no patch links were provided in the source data. The vulnerability is relevant to environments where Mkdocs with this plugin is used, particularly in automated documentation pipelines or CI/CD workflows that incorporate Markdown content inclusion from untrusted or external sources.

For European organizations, the impact of CVE-2025-59940 depends largely on their use of Mkdocs and the mkdocs-include-markdown-plugin in their documentation or development workflows. Organizations relying on automated documentation generation, especially those integrating external or user-supplied Markdown content, could face risks of integrity compromise where documentation is altered maliciously or unintentionally. This could lead to misinformation in technical documents, compliance reports, or user manuals, potentially affecting operational decisions or regulatory adherence. Additionally, availability impacts could disrupt documentation pipelines, delaying release cycles or internal communications. While confidentiality is not directly impacted, the integrity and availability concerns could affect sectors with stringent documentation requirements such as finance, healthcare, and critical infrastructure. The lack of required privileges and user interaction means attackers could exploit this remotely if the documentation build process is exposed or if malicious Markdown content is introduced into the source repositories. Given the reliance on open-source tooling in European tech ecosystems, this vulnerability could have a moderate operational impact if not addressed promptly.

European organizations should immediately upgrade the mkdocs-include-markdown-plugin to version 7.1.8 or later to remediate this vulnerability. Beyond upgrading, organizations should implement strict input validation and sanitization controls on all Markdown content sources, especially those that are external or user-generated, to prevent malicious content injection. Integrating static code analysis or content validation tools into CI/CD pipelines can help detect anomalous Markdown patterns before deployment. Restricting write access to documentation repositories and enforcing code review policies can reduce the risk of malicious content introduction. Additionally, organizations should monitor build logs and outputs for unexpected substitutions or errors that could indicate exploitation attempts. For environments where upgrading is delayed, isolating the documentation build process in sandboxed or containerized environments can limit potential impact. Finally, maintaining an inventory of systems using Mkdocs and this plugin will aid in rapid vulnerability management and patch deployment.