CVE-2026-11548 in WebSphere Application Server
Summary
by MITRE • 09/18/2026
IBM WebSphere Application Server and WebSphere Application Server Liberty are affected by an HTTP request smuggling vulnerability.
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Analysis
by VulDB Data Team • 09/18/2026
The identified security flaw within IBM WebSphere Application Server and WebSphere Application Server Liberty represents a critical class of vulnerabilities known as HTTP Request Smuggling, formally categorized under CWE-441: Unintended Interaction Between Components in the Same Security Context. This type of vulnerability arises when there is an inconsistency in how different network components interpret ambiguous or malformed HTTP request headers. In typical enterprise deployments involving IBM WebSphere products, these servers often sit behind reverse proxies, load balancers, or other front-end devices that terminate connections and forward requests to the backend application server. The core technical flaw lies in the discrepancy between how the front-end device parses specific header fields versus how the underlying WebSphere engine processes them. Specifically, this vulnerability is associated with improper handling of Transfer-Encoding headers, which are used to indicate the format of a message body. When an attacker crafts a request containing conflicting or malformed Transfer-Encoding values, such as combining chunked encoding with other content-length indicators in a way that violates strict RFC standards but exploits parsing ambiguities, the front-end proxy and the backend server may interpret the boundaries of individual requests differently.
From a technical perspective, this misalignment allows an attacker to inject malicious HTTP requests into the stream of legitimate traffic destined for internal applications or services behind the WebSphere instance. By carefully crafting the smuggled request, the adversary can bypass access controls that are enforced at the front-end layer but not validated by the backend application server. This effectively creates a tunnel through which unauthorized commands can be executed as if they originated from trusted sources within the network perimeter. The vulnerability leverages the fundamental principle of HTTP/1.1 message framing, where ambiguity in header interpretation leads to desynchronization between client and server state machines. In some configurations, this may also involve issues with how connection headers are managed during keep-alive sessions, allowing an attacker to manipulate session states or redirect traffic intended for one user to another. This mechanism is particularly dangerous because it exploits the trust relationship established by network infrastructure components that assume all incoming requests have been properly validated and sanitized before reaching the application layer.
The operational impact of this vulnerability is severe, potentially leading to unauthorized access to sensitive data, privilege escalation, or complete compromise of backend systems. An attacker could use HTTP request smuggling to perform cross-user attacks, where actions taken by one authenticated user are executed on behalf of another without their knowledge or consent. This can result in account takeover scenarios, allowing the adversary to view private information, modify critical business data, or initiate financial transactions under a victim's identity. Furthermore, if the backend services expose administrative interfaces or internal APIs that rely solely on front-end authentication checks, the attacker could gain direct access to these privileged endpoints. The ability to inject arbitrary requests also opens the door for further exploitation vectors, such as server-side request forgery (SSRF) attacks against internal resources that are not directly accessible from the external network. In environments where WebSphere Application Server Liberty is used in microservices architectures, this vulnerability could disrupt service mesh integrity and lead to broader systemic failures or data exfiltration across interconnected services.
Mitigation strategies must focus on eliminating ambiguity in HTTP request parsing and ensuring consistent interpretation of headers across all layers of the infrastructure. IBM has released patches for affected versions that address these specific header handling issues; therefore, applying the latest security updates is the primary remediation step. Administrators should ensure that both front-end proxies and backend WebSphere servers are configured to reject requests with ambiguous or malformed Transfer-Encoding fields rather than attempting to interpret them in potentially conflicting ways. It is also advisable to enforce strict HTTP/1.1 compliance by disabling support for older, less secure protocol versions if they are not strictly required. Network-level controls such as web application firewalls can be tuned to detect and block patterns associated with request smuggling attacks, although this should serve as a compensating control rather than the sole defense. Regular security assessments and penetration testing that specifically target HTTP desynchronization flaws will help identify residual risks in complex deployment topologies involving multiple intermediaries between clients and IBM WebSphere components.