CyberSecBulletin
CVE-2023-39962NVD status: Modified

security-advisories: Improper Access Control

Published Updated By the CyberSecBulletin desk

CVE-2023-39962 is a high-severity improper access control vulnerability in security-advisories from Nextcloud, with a CVSS 3.1 base score of 7.7 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected security-advisories versions: >= 19.0.0, < 19.0.13.10; >= 20.0.0, < 20.0.14.15; >= 21.0.0, < 21.0.9.13, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.02% chance of exploitation within 30 days, higher than 64% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update server to 19.0.13.0 or 20.0.14.15 or 21.0.9.13 or 22.2.10.14, whichever matches your release line, or a later version.
  2. Update Nextcloud Server to 19.0.13.10 or 20.0.14.15 or 21.0.9.13 or 22.2.10.14, whichever matches your release line, or a later version.
  3. Read the advisory on github.com for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
Nextcloudsecurity-advisories>= 19.0.0, < 19.0.13.10; >= 20.0.0, < 20.0.14.15; >= 21.0.0, < 21.0.9.13; >= 22.0.0, < 22.2.10.14; >= 23.0.0, < 23.0.12.9; >= 24.0.0, < 24.0.12.5; >= 25.0.0, < 25.0.9; >= 26.0.0, < 26.0.4; and 1 more rangesNot stated
Nextcloudserver19.0.0 up to, but not including, 19.0.13.0; 20.0.0 up to, but not including, 20.0.14.15; 21.0.0 up to, but not including, 21.0.9.13; 22.0.0 up to, but not including, 22.2.10.14; 23.0.0 up to, but not including, 23.0.12.9; 24.0.0 up to, but not including, 24.0.12.5; 25.0.0 up to, but not including, 25.0.9; 26.0.0 up to, but not including, 26.0.4; and 1 more ranges19.0.13.0, 20.0.14.15, 21.0.9.13, 22.2.10.14, 23.0.12.9, 24.0.12.5
NextcloudNextcloud Server19.0.0 up to, but not including, 19.0.13.10; 20.0.0 up to, but not including, 20.0.14.15; 21.0.0 up to, but not including, 21.0.9.13; 22.0.0 up to, but not including, 22.2.10.14; 23.0.0 up to, but not including, 23.0.12.9; 24.0.0 up to, but not including, 24.0.12.5; 25.0.0 up to, but not including, 25.0.9; 26.0.0 up to, but not including, 26.0.4; and 1 more ranges19.0.13.10, 20.0.14.15, 21.0.9.13, 22.2.10.14, 23.0.12.9, 24.0.12.5

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
ChangedThe attack can reach beyond the vulnerable component into other systems.
Confidentiality
NoneNo data is disclosed.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.17.7HighCNA (github.com)
CVSS 3.17.7HighNVD

Official description

Nextcloud Server provides data storage for Nextcloud, an open source cloud platform. Starting in version 19.0.0 and prior to versions 19.0.13.10, 20.0.14.15, 21.0.9.13, 22.2.10.14, 23.0.12.8, 24.0.12.5, 25.0.9, 26.0.4, and 27.0.1, a malicious user could delete any personal or global external storage, making them inaccessible for everyone else as well. Nextcloud server versions 25.0.9, 26.0.4, and 27.0.1 and Nextcloud Enterprise Server versions 19.0.13.10, 20.0.14.15, 21.0.9.13, 22.2.10.14, 23.0.12.9, 24.0.12.5, 25.0.9, 26.0.4, and 27.0.1 contain a patch for this issue. As a workaround, disable app files_external. This also makes the external storage inaccessible but retains the configurations until a patched version has been deployed.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Access Control

The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

How developers prevent this class of flaw

  • Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
  • Compartmentalize the system to have safe areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

More Improper Access Control vulnerabilities (CWE-284)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Other vulnerabilities in security-advisories

All security-advisories vulnerabilities

Recent Improper Access Control vulnerabilities

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