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Security Bulletin: IBM WebSphere Application Server and WebSphere Application Server Liberty are affected by an uncontrolled resource consumption due to js-yaml (CVE-2026-84375)

Security Bulletin


Summary

There is a vulnerability in the js-yaml library that affects IBM WebSphere Application Server and WebSphere Application Server Liberty.

Vulnerability Details

CVEID:   CVE-2026-84375
DESCRIPTION:   js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2, 4.3.2, and 5.4.1, maxTotalMergeKeys in lib/js-yaml/loader.js and lib/loader.js does not count empty mapping sources while processing the merge key . An attacker can alias a large sequence of empty mappings into many merge targets, causing O(N * K) processing while totalMergeKeys remains unchanged and the configured resource limit is never reached. A relatively small YAML document can therefore cause prolonged CPU consumption in applications that parse untrusted YAML, and merge processing is enabled by default on these release lines. In v3 & v4, merge is enabled by default so the severity score is higher. This issue is fixed in versions 3.15.2, 4.3.2, and 5.4.1.
CWE:   CWE-400: Uncontrolled Resource Consumption
CVSS Source:   security-advisories@github.com
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Affected Products and Versions

 

Affected Product(s)Version(s)
WebSphere Application Server9.0
WebSphere Application Server - Liberty17.0.0.3 - 26.0.0.10

Remediation/Fixes

IBM strongly recommends addressing the vulnerability now by applying a currently available interim fix or fix pack that contains the fix for APAR DT503710 or DT504247. To determine if a feature is enabled for WebSphere Application Server Liberty, refer to How to determine if Liberty is using a specific feature. 

For IBM WebSphere Application Server Liberty 17.0.0.3 - 26.0.0.10 using apiDiscovery-1.0 feature:

· Upgrade to minimal fix pack levels as required by the interim fix and then apply the Interim Fix that resolves DT503710
--OR--
· Apply Fix Pack 26.0.0.11 or later (targeted availability 4Q2026).

For IBM WebSphere Application Server traditional:

For V9.0.0.0 through 9.0.5.29:
· Upgrade to minimal fix pack levels as required by the interim fix and then apply the Interim Fix that resolves DT504247 
--OR--
· Apply Fix Pack 9.0.5.30 or later (targeted availability 4Q2026).  

Additional interim fixes may be available and linked off the interim fix download page.

Workarounds and Mitigations

None

Get Notified about Future Security Bulletins

References

Off

To determine if a feature is enabled for WebSphere Application Server Liberty, refer to How to determine if Liberty is using a specific feature. 

Acknowledgement

Change History

13 Oct 2026: Initial Publication
15 Oct 2026: Updated affected Liberty feature

*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.

Disclaimer

According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.

Document Location

Worldwide

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Document Information

Modified date:
15 October 2026

Initial Publish date:
13 October 2026

UID

ibm17292227