CVE-2026-91197 in Engine
Summary
by MITRE • 09/15/2026
Flowable flowable-engine through 8.0.0 contains an XML external entity injection vulnerability in ProcessDiagramLayoutFactory.parseXml() that fails to disable external entity resolution when parsing deployed BPMN resources. Attackers with process deployment privileges can embed DOCTYPE declarations with external entities in BPMN files to read arbitrary local files or trigger requests to internal network endpoints when diagram layout is computed.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified within Flowable engine versions up to 8.0.0 represents a critical XML External Entity injection flaw located specifically in the ProcessDiagramLayoutFactory.parseXml method. This component is responsible for parsing BPMN resources, which are standard files used to define business process models and workflows. The core technical deficiency lies in the failure of the XML parser configuration to disable external entity resolution by default when processing these deployed artifacts. In a secure implementation, parsers should strictly adhere to safe defaults that prohibit the loading or resolving of entities defined outside the immediate document scope unless explicitly authorized for specific trusted use cases. By leaving this capability enabled, the application inadvertently creates an attack surface where maliciously crafted XML structures can exploit the underlying parsing library's behavior to execute unintended operations beyond simple data representation.
The operational impact of this vulnerability is significant because it allows attackers who possess process deployment privileges to compromise the integrity and confidentiality of the system environment. By embedding a DOCTYPE declaration containing external entity definitions within a BPMN file, an attacker can instruct the server-side parser to fetch resources from arbitrary local paths or remote network endpoints. This capability effectively transforms the application into a proxy for reading sensitive files on the host operating system, such as configuration files with database credentials or private keys, thereby leading to unauthorized data disclosure. Furthermore, if the underlying environment permits outbound connections, this flaw can be leveraged to perform server-side request forgery against internal network services that may not have proper authentication mechanisms in place, potentially facilitating further lateral movement within a corporate network infrastructure.
From a classification perspective, this vulnerability aligns with CWE-611, which describes Improper Restriction of XML External Entity Reference. This category encompasses issues where an application processes external entities without adequate validation or restriction, allowing attackers to manipulate the parsing process for malicious ends. In terms of offensive security frameworks, this exploit technique corresponds to ATT&CK tactic T1552, specifically sub-technique T1552.004 involving Unsecured Credentials found in local system images, as well as aspects of T1071 Application Layer Protocol if used for exfiltration or command and control via HTTP requests triggered by the entity resolution. The vulnerability highlights a common misconfiguration pattern where developers assume that input from trusted sources like internal process deployments does not require rigorous sanitization, overlooking the powerful capabilities inherent in XML parsing libraries when external entities are permitted.
Mitigation strategies must focus on hardening the XML parser configuration used within the Flowable engine to enforce strict security defaults. The primary remediation involves explicitly disabling DTDs and external entity resolution at the parser level before any BPMN files are processed. This can typically be achieved by setting specific features or properties in the underlying JAXP or DOM/SAX parsers, such as preventing access to external general entities and external parameter entities. Additionally, organizations should implement input validation checks that reject XML documents containing DOCTYPE declarations unless absolutely necessary for legitimate functionality, which is rarely the case for standard BPMN diagrams. Regular security audits of third-party libraries used in workflow engines are essential to ensure they do not contain known vulnerabilities related to XML parsing, and developers must be trained on secure coding practices regarding XML processing to prevent similar injection flaws in future development cycles.