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

Source: https://junglewise.ai/threats/cve-2026-15634-ibm-websphere-application-server-http-request-smuggling-via  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-14. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

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](https://junglewise.ai/threats/technologies/websphere-application-server), [IBM WebSphere Application Server Liberty](https://junglewise.ai/threats/technologies/websphere-application-server-liberty). Vendors: [IBM](https://junglewise.ai/threats/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](https://www.ibm.com/support/pages/node/7286610)

## Related threats

- [IBM WebSphere Application Server Liberty information disclosure in JMX REST connector](https://junglewise.ai/threats/cve-2026-78636-ibm-websphere-application-server-liberty-17-0-0-3-through-26-0-0)
- [IBM WebSphere Application Server Liberty server-side request forgery in Admin Center](https://junglewise.ai/threats/cve-2026-11547-ibm-websphere-application-server-liberty-17-0-0-3-through-26-0-0)
- [IBM WebSphere Application Server Liberty open redirect](https://junglewise.ai/threats/cve-2026-10844-ibm-websphere-application-server-liberty-17-0-0-3-through-26-0-0)
- [IBM WebSphere Application Server Liberty information disclosure](https://junglewise.ai/threats/cve-2026-108284-ibm-websphere-application-server-liberty-17-0-0-3-through-26-0-0)
- [IBM WebSphere Application Server Liberty information disclosure](https://junglewise.ai/threats/cve-2026-103320-ibm-websphere-application-server-liberty-17-0-0-3-through-26-0-0)