What’s Vulnerable › Vulnerabilities
CVE-2026-47857: Reactor Core windowTimeout fair-backpressure stream hang due to 20-bit index wrap-around
- Severity: medium (CVSS 5.9 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-08-27 · updated 2026-09-04
- Weakness: CWE-190
Description
In Reactor Core, applications that use the Flux.windowTimeout operator with fairBackpressure enabled are vulnerable to a Denial of Service (DoS) condition. Reactor Core 3.8.0 - 3.8.6 Reactor Core 3.5.0 - 3.7.19 Reactor Core 3.4.41 and earlier
Affected products
- Spring Reactor Core: before 3.4.42; from 3.5.0 before 3.7.20; from 3.8.0 before 3.8.6.1 — fixed in 3.4.42, 3.7.20, 3.8.6.1
How to fix
Upgrade to a fixed version: Spring Reactor Core 3.4.42, 3.7.20, 3.8.6.1. Check the vendor advisory for mitigations.
References
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