CVE-2021-22896Network attack vector

Cross-user alias creation via unchecked account ID

Published Jun 11, 2021 · Updated Aug 3, 2024

Improper access control in Nextcloud Mail before 1.9.5 allows remote authenticated users to create mail aliases for other users. The alias-creation request accepted a caller-supplied account identifier without checking that the referenced mail account belonged to the authenticated user. Any signed-in Mail user who can reach the alias endpoint can modify another user's mail identity by attaching an unauthorized alias.

CVSS severity4.3
Medium
EPSS probability0.99%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper access control in Nextcloud Mail before 1.9.5 allows remote authenticated users to create mail aliases for other users. The alias-creation request accepted a caller-supplied account identifier without checking that the referenced mail account belonged to the authenticated user. Any signed-in Mail user who can reach the alias endpoint can modify another user's mail identity by attaching an unauthorized alias.

The record

CVE
CVE-2021-22896
Published
Jun 11, 2021
Updated
Aug 3, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Mail
Classifications
CWE-862, CWE-284, T1098
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

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

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Fixed in 1.9.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Mailversion=Fixed in 1.9.5

Published CVSS scores

4.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:S/C:N/I:P/A:N
4.3NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-862Missing Authorization
CWE-284Improper Access Control
T1098Account Manipulation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo