Is CVE-2026-15396 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-15396 being exploited in the wild.

How severe is CVE-2026-15396?

Medium severity, with a CVSS score of 6.5, published 14 September 2026.

Which products and versions are affected?

IBM WebSphere Application Server 9.0 prior to 9.0.5.29, 8.5 prior to 8.5.5.31; IBM WebSphere Application Server Liberty affected versions not explicitly stated.

Is there a fix for CVE-2026-15396?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-15396 attacked?

It is attacked over the network.

Am I affected by CVE-2026-15396?

Check whether you run IBM WebSphere Application Server or IBM WebSphere Application Server Liberty at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-15396: IBM WebSphere Application Server HTTP request smuggling via transfer-encoding

CVE-2026-15396 · Severity: medium · CVSS 6.5 · Published 2026-09-14

IBM WebSphere Application Server is a Java-based middleware platform used to host enterprise web applications. This vulnerability allows an attacker to manipulate how HTTP requests are interpreted by sending specially crafted transfer-encoding headers, enabling cache poisoning, firewall bypass, and cross-site scripting attacks without requiring authentication.

Technologies: IBM WebSphere Application Server, IBM WebSphere Application Server Liberty. Vendors: IBM.

Quick answers

Is CVE-2026-15396 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-15396 being exploited in the wild.
How severe is CVE-2026-15396?: Medium severity, with a CVSS score of 6.5, published 14 September 2026.
Which products and versions are affected?: IBM WebSphere Application Server 9.0 prior to 9.0.5.29, 8.5 prior to 8.5.5.31; IBM WebSphere Application Server Liberty affected versions not explicitly stated.
Is there a fix for CVE-2026-15396?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-15396 attacked?: It is attacked over the network.
Am I affected by CVE-2026-15396?: Check whether you run IBM WebSphere Application Server or IBM WebSphere Application Server Liberty at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

This is an HTTP request smuggling vulnerability (CWE-444) caused by improper parsing of the HTTP transfer-encoding request header in the request processing logic. The vulnerability affects WebSphere Application Server 9.0 prior to 9.0.5.29 and 8.5 prior to 8.5.5.31, as well as WebSphere Application Server Liberty. An unauthenticated attacker on the network can send a specially crafted transfer-encoding header to create a discrepancy between how the application server and upstream proxies/caches interpret the request boundary, allowing request smuggling attacks. Successful exploitation enables cache poisoning, web application firewall bypass, and XSS injection. IBM has issued patches in versions 9.0.5.29 and 8.5.5.31.

Affected products

IBM WebSphere Application Server 9.0 prior to 9.0.5.29, 8.5 prior to 8.5.5.31
IBM WebSphere Application Server Liberty affected versions not explicitly stated

Timeline

2026-09-14: disclosed

References

https://www.ibm.com/support/pages/node/7286610

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