CVE-2021-22878Public exploitNetwork attack vector

Reflected XSS via unescaped rename error

Published Mar 3, 2021 · Updated Aug 3, 2024

Reflected XSS in Nextcloud Server before 20.0.6 allows remote authenticated users to execute script through a crafted filename rename error. OC.Notification.show passed the resulting error text to showMessage without HTML escaping, causing markup in the filename to become executable DOM content. Exploitation requires a crafted filename, a failed rename, and browser interaction; Nextcloud's strict Content Security Policy substantially limits the resulting script behavior.

CVSS severity4.8
Medium
EPSS probability1.06%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in Nextcloud Server before 20.0.6 allows remote authenticated users to execute script through a crafted filename rename error. OC.Notification.show passed the resulting error text to showMessage without HTML escaping, causing markup in the filename to become executable DOM content. Exploitation requires a crafted filename, a failed rename, and browser interaction; Nextcloud's strict Content Security Policy substantially limits the resulting script behavior.

The record

CVE
CVE-2021-22878
Published
Mar 3, 2021
Updated
Aug 3, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Server
Classifications
CWE-79
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 3, 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 20.0.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Serverversion=Fixed in 20.0.6

Published CVSS scores

4.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/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 exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Public exploit references

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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