Reactor Core windowTimeout fair-backpressure stream hang due to 20-bit index wrap-around (CVE-2026-47857) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-47857

Reactor Core windowTimeout fair-backpressure stream hang due to 20-bit index wrap-around

Answer in brief

CVE-2026-47857 records a Unknown severity vulnerability in Reactor Core windowTimeout fair-backpressure stream hang due to 20-bit index wrap-around. The current sources do not mark it as known exploited. The current feed maps Spring/Reactor Core (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 26, 2026Updated Aug 26, 2026Source checked Aug 27, 2026First seen by HOL Aug 27, 2026Material review Aug 26, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Spring/Reactor Core (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Spring/Reactor Coregeneric	3.8.0 \|\| 3.5.0 \|\| 0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Spring/Reactor Core.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Aug 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 27, 2026

Sources and claim methodology

Source referencespring.io

Upstream source 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

Quoted source text, attributed separately from HOL analysis.