CVE-2026-16180 in App Connect Enterprise
Summary
by MITRE • 09/04/2026
IBM App Connect Enterprise 13.0.1.0 through 13.0.8.1, and 12.0.1.0 through 12.0.12.28 and IBM Integration Bus for z/OS 10.1.0.0 through 10.1.0.7 Toolkit could allow an authenticated user to cause a denial-of-service condition due to improper validation of XML entities.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in IBM App Connect Enterprise and IBM Integration Bus for z/OS represents a significant risk related to the processing of Extensible Markup Language, specifically concerning the handling of external entity references. This flaw exists within versions 13.0.1.0 through 13.0.8.1, as well as earlier iterations ranging from 12.0.1.0 up to 12.0.12.28 for App Connect Enterprise and version 10.1.0.0 through 10.1.0.7 of the IBM Integration Bus Toolkit for z/OS environments. The core technical deficiency lies in the improper validation or sanitization of XML entities when they are parsed by the application engine. In standard XML processing, parsers can be configured to resolve external entity references, which allows an XML document to request data from a specified Uniform Resource Identifier. When this feature is not properly restricted or validated against malicious inputs, it creates an avenue for exploitation that targets the underlying system resources rather than compromising confidentiality or integrity directly in the traditional sense.
An authenticated user can exploit this vulnerability by crafting and submitting specially formatted XML documents containing recursive external entity definitions or excessively large entity expansions. This technique leverages what is commonly known as a Billion Laughs attack, also referred to as an exponential entity expansion. By defining entities that reference other entities which in turn reference more entities, the parser attempts to expand these references into memory during the parsing process. Because IBM App Connect Enterprise and Integration Bus are designed to handle complex integration workflows involving large volumes of data exchange, they may allocate significant amounts of system resources to resolve these expansions. The improper validation means the application does not adequately check for depth limits or size constraints before processing the entity resolution requests. Consequently, this leads to a rapid consumption of available memory and CPU cycles as the parser struggles to expand the nested structures indefinitely until it exhausts its allocated resources.
The operational impact of this vulnerability is primarily characterized by a denial-of-service condition affecting the affected IBM integration platforms. When an authenticated attacker triggers this resource exhaustion, the application process may become unresponsive or crash entirely due to out-of-memory errors. In enterprise environments where these tools serve as critical middleware for connecting disparate systems and applications, such instability can disrupt business continuity. It prevents legitimate users from accessing services routed through the affected instance and can cause cascading failures if other dependent systems rely on the availability of this integration layer. While the vulnerability requires authentication to exploit, which limits its scope compared to remote unauthenticated attacks, it remains severe because internal threats or compromised credentials within an organization could easily trigger service outages. The impact is strictly limited to availability, as there is no indication that this flaw allows for arbitrary code execution or unauthorized data access beyond what the authenticated user already possesses.
From a classification perspective, this vulnerability aligns with CWE-778: Insufficient Regular Expression Validation in XML Processing and more broadly falls under CWE-400: Uncontrolled Resource Consumption. It is also associated with ATT&CK technique T1496: Resource Hijacking, specifically the sub-technique of CPU or memory exhaustion through resource-intensive operations. To mitigate this risk, organizations must apply the latest security patches provided by IBM for their specific versions of App Connect Enterprise and Integration Bus for z/OS. Beyond patching, administrators should enforce strict input validation policies on all XML inputs processed by these systems. This includes disabling external entity resolution if it is not explicitly required for business operations, configuring parsers to limit entity expansion depth and size, and implementing network-level controls such as rate limiting or web application firewalls that can detect and block anomalous XML payloads before they reach the application layer. Regular auditing of integration flows should also be conducted to ensure no legacy configurations inadvertently enable vulnerable parsing behaviors.