CVE-2022-23640 is a vulnerability classified under CWE-611, which pertains to the improper restriction of XML External Entity (XXE) references. This vulnerability affects the monitorjbl excel-streaming-reader library, a Java-based streaming Excel reader built on top of Apache POI. Versions prior to 2.1.0 of the xlsx-streamer component do not properly configure the XML parser to disable or restrict external entity processing. As a result, maliciously crafted Excel files containing XML External Entity references can trigger XML Entity Expansion or XXE attacks when parsed by vulnerable versions of the library. This can lead to several security issues including disclosure of local files, server-side request forgery (SSRF), denial of service (via entity expansion), or other impacts depending on the XML parser's behavior and the environment in which the library is used. The vulnerability was addressed in version 2.1.0 by applying the necessary XML parser settings to prevent these attacks. There are no known workarounds other than upgrading to the patched version. No exploits have been observed in the wild to date. The vulnerability is medium severity, reflecting the moderate risk posed by XXE issues when exploited in certain contexts. The vulnerability is particularly relevant for applications and services that process untrusted Excel files using the affected library versions, as they may be exposed to XML-based attacks that compromise confidentiality, integrity, or availability of the system or data.

For European organizations, the impact of CVE-2022-23640 depends largely on the extent to which they use the vulnerable excel-streaming-reader library in their software stacks, especially in applications that handle untrusted or user-uploaded Excel files. Exploitation could lead to unauthorized disclosure of sensitive internal files, potentially exposing confidential business or personal data. Additionally, attackers could leverage SSRF capabilities to pivot into internal networks, increasing the risk of further compromise. Denial of service attacks could disrupt critical business processes relying on Excel data ingestion. Sectors such as finance, healthcare, government, and manufacturing—where Excel is commonly used for data exchange and reporting—may be particularly at risk if their software incorporates the vulnerable library. Given the lack of known exploits, the immediate threat is moderate, but the potential for impactful attacks exists if threat actors develop exploits. The vulnerability could also be leveraged in targeted attacks against European organizations with high-value data or critical infrastructure, especially if combined with social engineering to deliver malicious Excel files. Overall, the vulnerability poses a moderate risk to confidentiality, integrity, and availability, with the potential for significant impact in environments processing untrusted Excel documents.

The primary and most effective mitigation is to upgrade all instances of the monitorjbl excel-streaming-reader library to version 2.1.0 or later, where the XML parser is properly configured to prevent XXE attacks. Organizations should conduct an inventory of software components to identify usage of the vulnerable library versions. For applications that cannot be immediately upgraded, consider implementing strict input validation and sanitization on Excel files before processing, including scanning for suspicious XML entities or external references. Employ runtime application security controls such as sandboxing or running parsers with least privilege to limit the impact of potential exploitation. Network-level controls can also help, such as restricting outbound HTTP requests from servers processing Excel files to prevent SSRF exploitation. Monitoring and logging of XML parsing errors and unusual file processing behavior can aid in early detection of exploitation attempts. Finally, educate developers and security teams about the risks of XXE vulnerabilities and the importance of secure XML parser configurations in all components handling XML data.