CVE-2026-59725Network attack vector

Service interruption via unclosed polling responses

Published Jul 8, 2026 · Updated Jul 8, 2026

Resource exhaustion in Socket.IO Engine.IO 4.1.0 through 6.6.6 allows remote attackers to interrupt service via malformed polling requests. The protocol-v4 polling POST handler in polling.ts reports invalid application/octet-stream content but returns without ending the HTTP response. No authentication or user interaction is required; repeated sessions retain server sockets and file descriptors until legitimate clients cannot connect.

CVSS severity7.5
High
EPSS probability0.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Socket.IO Engine.IO 4.1.0 through 6.6.6 allows remote attackers to interrupt service via malformed polling requests. The protocol-v4 polling POST handler in polling.ts reports invalid application/octet-stream content but returns without ending the HTTP response. No authentication or user interaction is required; repeated sessions retain server sockets and file descriptors until legitimate clients cannot connect.

The record

CVE
CVE-2026-59725
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
Socket.IO
Product
Socket.IO
Classifications
CWE-404, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 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=>= 4.1.0, < 6.6.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Socket.IO · Socket.IOversion=>= 4.1.0, < 6.6.7

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/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.

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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-404Improper Resource Shutdown or Release
T1499.003Application Exhaustion Flood

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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