Is CVE-2026-15634 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-15634 being exploited in the wild.

How severe is CVE-2026-15634?

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

Which products and versions are affected?

IBM WebSphere Application Server 8.5 prior to 8.5.5.31, 9.0 prior to 9.0.5.29; IBM WebSphere Application Server Liberty prior to 9.0.5.29 and 8.5.5.31.

Is there a fix for CVE-2026-15634?

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-2026-15634 attacked?

It is attacked over the network.

Am I affected by CVE-2026-15634?

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-2026-15634: IBM WebSphere Application Server HTTP request smuggling via transfer-encoding header

CVE-2026-15634 · Severity: medium · CVSS 6.5 · Published 2026-09-14

IBM WebSphere Application Server is a Java-based middleware platform used to run mission-critical enterprise applications. An attacker can send specially crafted HTTP requests that exploit improper parsing of the transfer-encoding header, allowing them to poison web caches, bypass firewalls, and inject malicious content that targets end users. This could lead to data theft, defacement, or credential compromise.

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

Quick answers

Is CVE-2026-15634 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-15634 being exploited in the wild.
How severe is CVE-2026-15634?: Medium severity, with a CVSS score of 6.5, published 14 September 2026.
Which products and versions are affected?: IBM WebSphere Application Server 8.5 prior to 8.5.5.31, 9.0 prior to 9.0.5.29; IBM WebSphere Application Server Liberty prior to 9.0.5.29 and 8.5.5.31.
Is there a fix for CVE-2026-15634?: 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-2026-15634 attacked?: It is attacked over the network.
Am I affected by CVE-2026-15634?: 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

CVE-2026-15634 is an HTTP request smuggling vulnerability (CWE-444) in IBM WebSphere Application Server and WebSphere Liberty, caused by inconsistent parsing of the HTTP transfer-encoding request header. An attacker can craft a malicious HTTP request with a specially formed transfer-encoding header that is interpreted differently by the application server and downstream proxies or caches. The attack is network-accessible and requires no authentication or user interaction. Successful exploitation allows cache poisoning, web application firewall bypass, and cross-site scripting (XSS) attacks. Patches are available: WebSphere AS 9.0.5.29 and 8.5.5.31 or later resolve this issue.

Affected products

IBM WebSphere Application Server 8.5 prior to 8.5.5.31, 9.0 prior to 9.0.5.29
IBM WebSphere Application Server - Liberty prior to 9.0.5.29 and 8.5.5.31

Timeline

2026-09-14: disclosed

References

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

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