CVE-2026-40986: Spring Web Flow JS RemotingHandler renders non-HTML Response as HTML

Severity: medium (CVSS 4.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-11 · updated 2026-09-04
Weakness: CWE-79

Description

Spring Web Flow's JavaScript RemotingHandler renders the body of an error response as HTML even when the response is not "text/html", which can result in a scripting attack in the user's browser if the error response from the server contains error details with input reflected from an attacker. Affected versions: Spring Web Flow 4.0.0; 3.0.0 through 3.0.1; 2.5.0 through 2.5.1.

Affected products

Spring Web Flow: before 2.5.2; from 3.0.0 before 3.0.1.1; 4.0.0 — fixed in 2.5.2, 3.0.1.1

How to fix

Upgrade to a fixed version: Spring Web Flow 2.5.2, 3.0.1.1. Check the vendor advisory for mitigations.

References

https://spring.io/security/cve-2026-40986

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