CVE-2026-47857Network attack vector

Stream hang via 20-bit index wrap-around

Published Aug 26, 2026 · Updated Aug 27, 2026

Denial of service in affected Spring Reactor Core releases allows remote attackers to hang reactive streams through network traffic. The Flux.windowTimeout fair-backpressure path stores progress in a 20-bit index that wraps during extended processing, permanently stopping element delivery without an error. Exploitation requires fairBackpressure, a long-lived stream, and specific downstream backpressure; controlled connection duration and read speed drive resource exhaustion.

CVSS severity5.9
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in affected Spring Reactor Core releases allows remote attackers to hang reactive streams through network traffic. The Flux.windowTimeout fair-backpressure path stores progress in a 20-bit index that wraps during extended processing, permanently stopping element delivery without an error. Exploitation requires fairBackpressure, a long-lived stream, and specific downstream backpressure; controlled connection duration and read speed drive resource exhaustion.

The record

CVE
CVE-2026-47857
Published
Aug 26, 2026
Updated
Aug 27, 2026
Vendor
Spring
Product
Reactor Core
Classifications
CWE-190, T1499.003
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 <=3.4.41
  2. Affected versionversion=3.5.0 <=3.7.19
  3. Affected versionversion=3.8.0 <=3.8.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Spring · Reactor Coreversion=0 <=3.4.41; version=3.5.0 <=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-190Integer Overflow or Wraparound
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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