CVE-2021-40539Known exploitationPublic exploitNetwork attack vector

Unauthenticated code execution via URL normalization error

Published Sep 7, 2021 · Updated Oct 21, 2025

Authentication bypass in Zoho ManageEngine ADSelfService Plus 6113 and earlier allows remote attackers to execute arbitrary commands. The REST API security filter validates specially crafted URLs before normalizing them, so alternate path forms reach protected endpoints and permit arbitrary file upload. No credentials or user interaction are required; successful requests can execute uploaded code with the service account privileges.

CVSS severity9.8
Critical
EPSS probability98.96%
Next 30 days · Nov 1, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Zoho ManageEngine ADSelfService Plus 6113 and earlier allows remote attackers to execute arbitrary commands. The REST API security filter validates specially crafted URLs before normalizing them, so alternate path forms reach protected endpoints and permit arbitrary file upload. No credentials or user interaction are required; successful requests can execute uploaded code with the service account privileges.

The record

CVE
CVE-2021-40539
Published
Sep 7, 2021
Updated
Oct 21, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-706, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 22, 2021Exploitation reportedDEV-0322 targeted exploitation campaign
  3. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

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.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsShadowserver observations through Sep 28, 2026. Gaps indicate unavailable data.
Sep 22, 2026Sep 28, 2026
View daily counts
Reporting dayUnique IPs
Sep 22, 20262
Sep 23, 20262
Sep 24, 202612
Sep 25, 20262
Sep 26, 20263
Sep 27, 20262
Sep 28, 20263
Latest reporting daySep 28, 2026
Latest daily unique IPs3
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-706Use of Incorrectly-Resolved Name or Reference
T1190Exploit Public-Facing Application

Public exploit references

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

Reported exploitation

Technologies

Your stack

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Your stack

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