CVE-2021-4236Network attack vector

Authentication bypass via skipped WebSocket hook

Published Dec 27, 2022 · Updated Apr 11, 2025

Authentication bypass in Ian Spence Web 1.4.0 through 1.5.1 allows remote attackers to enter protected WebSocket handlers. Server.socketHandler upgrades the connection without invoking the configured AuthenticateMethod, then calls the handler with nil UserData. Only applications that register WebSocket routes with an AuthenticateMethod hook are exposed; unauthenticated access can bypass handler authorization or trigger a nil-pointer panic.

CVSS severity9.8
Critical
EPSS probability1.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Ian Spence Web 1.4.0 through 1.5.1 allows remote attackers to enter protected WebSocket handlers. Server.socketHandler upgrades the connection without invoking the configured AuthenticateMethod, then calls the handler with nil UserData. Only applications that register WebSocket routes with an AuthenticateMethod hook are exposed; unauthenticated access can bypass handler authorization or trigger a nil-pointer panic.

The record

CVE
CVE-2021-4236
Published
Dec 27, 2022
Updated
Apr 11, 2025
Vendor
Ian Spence
Product
Web
Classifications
CWE-476, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 27, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 11, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=1.4.0 <1.5.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Ian Spence · Webversion=1.4.0 <1.5.2

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-476NULL Pointer Dereference
T1190Exploit Public-Facing Application

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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