CVE-2021-22906Network attack vector

Temporary file denial via unauthorized locking

Published Jun 11, 2021 · Updated Aug 3, 2024

Improper access control in Nextcloud End-to-End Encryption before 1.5.3, 1.6.3, and 1.7.1 allows remote authenticated users to lock others' files. The folder-locking API accepts a target file identifier without verifying that the authenticated account owns or may control that file. Any logged-in account can therefore prevent another user from accessing or updating affected files until the unauthorized lock is cleared, causing a temporary service interruption without reported data disclosure or modification.

CVSS severity6.5
Medium
EPSS probability0.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Nextcloud End-to-End Encryption before 1.5.3, 1.6.3, and 1.7.1 allows remote authenticated users to lock others' files. The folder-locking API accepts a target file identifier without verifying that the authenticated account owns or may control that file. Any logged-in account can therefore prevent another user from accessing or updating affected files until the unauthorized lock is cleared, causing a temporary service interruption without reported data disclosure or modification.

The record

CVE
CVE-2021-22906
Published
Jun 11, 2021
Updated
Aug 3, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud End-to-End Encryption
Classifications
CWE-639, CWE-284, CWE-400, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=Fixed in 1.5.3, 1.6.3, 1.7.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud End-to-End Encryptionversion=Fixed in 1.5.3, 1.6.3, 1.7.1

Published CVSS scores

4.0NVDAV:N/AC:L/Au:S/C:N/I:N/A:P
6.5NVDCVSS:3.1/AV:N/AC:L/PR:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-639Authorization Bypass Through User-Controlled Key
CWE-284Improper Access Control
CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

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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