CVE-2021-29438Network attack vector

Cross-site scripting via insufficient toast escaping

Published Apr 13, 2021 · Updated Aug 3, 2024

Cross-site scripting in Nextcloud Dialogs before 3.1.2 allows remote authenticated users to execute script in another user's browser via crafted toast text. The toast helpers insufficiently escape script-related characters in text supplied by a consuming application before rendering that text. Exploitation requires user-controlled input to reach a toast and another user to view it; Nextcloud Server's strict content security policy limits the resulting risk.

CVSS severity4.6
Medium
EPSS probability0.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Nextcloud Dialogs before 3.1.2 allows remote authenticated users to execute script in another user's browser via crafted toast text. The toast helpers insufficiently escape script-related characters in text supplied by a consuming application before rendering that text. Exploitation requires user-controlled input to reach a toast and another user to view it; Nextcloud Server's strict content security policy limits the resulting risk.

The record

CVE
CVE-2021-29438
Published
Apr 13, 2021
Updated
Aug 3, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Dialogs
Classifications
CWE-79, CWE-80
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 13, 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=< 3.1.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Dialogsversion=< 3.1.2

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.6GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/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 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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

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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