CVE-2026-47863Network attack vector

Stream hang via unscheduled residual-buffer timeout

Published Aug 26, 2026 · Updated Aug 27, 2026

Race condition in Flux.bufferTimeout in Spring Reactor Core 3.7.19 and earlier or 3.8.0 through 3.8.6 allows remote attackers to hang streams. During a flush, FluxBufferTimeout cancels the active timer, then accepts residual upstream items without rearming it, leaving buffered items indefinitely unprocessed. Reachability requires fairBackpressure to be enabled and attacker influence over upstream delivery timing; the affected pipeline stops processing and can exhaust resources.

CVSS severity5.9
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in Flux.bufferTimeout in Spring Reactor Core 3.7.19 and earlier or 3.8.0 through 3.8.6 allows remote attackers to hang streams. During a flush, FluxBufferTimeout cancels the active timer, then accepts residual upstream items without rearming it, leaving buffered items indefinitely unprocessed. Reachability requires fairBackpressure to be enabled and attacker influence over upstream delivery timing; the affected pipeline stops processing and can exhaust resources.

The record

CVE
CVE-2026-47863
Published
Aug 26, 2026
Updated
Aug 27, 2026
Vendor
Spring
Product
Reactor Core
Classifications
CWE-835, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=3.7.19
  2. Affected versionversion=3.8.0 <=3.8.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Spring · Reactor Coreversion=0 <=3.7.19; version=3.8.0 <=3.8.6

Published CVSS scores

5.9VMware CNACVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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