CVE-2023-39961Network attack vector

Image disclosure via omitted share permission lookup

Published Aug 10, 2023 · Updated Oct 10, 2024

Improper access control in affected Nextcloud Server releases allows remote authenticated users to download restricted shared images. The Text app's attachment resolver retrieves an image by file identifier without fetching the enclosing share's download permission, so inline embedding bypasses the restriction. Exploitation requires an authenticated recipient, a viewable share with downloads disabled, and permission to create or edit a text file; the result is disclosure of shared image content.

CVSS severity3.5
Low
EPSS probability0.58%
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 affected Nextcloud Server releases allows remote authenticated users to download restricted shared images. The Text app's attachment resolver retrieves an image by file identifier without fetching the enclosing share's download permission, so inline embedding bypasses the restriction. Exploitation requires an authenticated recipient, a viewable share with downloads disabled, and permission to create or edit a text file; the result is disclosure of shared image content.

The record

CVE
CVE-2023-39961
Published
Aug 10, 2023
Updated
Oct 10, 2024
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-284, T1213
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 10, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 10, 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=>= 24.0.4, < 24.0.12.5
  2. Affected versionversion=>= 25.0.0, < 25.0.9
  3. Affected versionversion=>= 26.0.0, < 26.0.4
  4. Affected versionversion=>= 27.0.0, < 27.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Security Advisoriesversion=>= 24.0.4, < 24.0.12.5; version=>= 25.0.0, < 25.0.9; version=>= 26.0.0, < 26.0.4; version=>= 27.0.0, < 27.0.1

Published CVSS scores

3.5NextcloudCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N
3.5NISTCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/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-284Improper Access Control
T1213Data from Information Repositories

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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