CyberSecBulletin
CVE-2023-35927NVD status: Modified

security-advisories: Improper Access Control

Published Updated By the CyberSecBulletin desk

CVE-2023-35927 is a high-severity improper access control vulnerability in security-advisories from Nextcloud, with a CVSS 3.1 base score of 8.1 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: Nextcloud Server >= 25.0.0, < 25.0.7; Nextcloud Server >= 26.0.0, < 26.0.2; Nextcloud Enterprise Server >= 25.0.0, < 25.0.7, 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 0.8% chance of exploitation within 30 days, higher than 57% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Nextcloud Server to 19.0.13.9 or 20.0.14.14 or 21.0.9.12 or 22.2.10.12, whichever matches your release line, or a later version.
  2. Read the advisory on github.com for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
Nextcloudsecurity-advisoriesNextcloud Server >= 25.0.0, < 25.0.7; Nextcloud Server >= 26.0.0, < 26.0.2; Nextcloud Enterprise Server >= 25.0.0, < 25.0.7; Nextcloud Enterprise Server >= 26.0.0, < 26.0.2; Nextcloud Enterprise Server >= 21.0.0, < 21.0.9.12; Nextcloud Enterprise Server >= 22.0.0, < 22.2.10.12; Nextcloud Enterprise Server >= 23.0.0, < 23.0.12.7; Nextcloud Enterprise Server >= 24.0.0, < 24.0.12.2Not stated
NextcloudNextcloud Server16.0.0 up to, but not including, 19.0.13.9; 20.0.0 up to, but not including, 20.0.14.14; 21.0.0 up to, but not including, 21.0.9.12; 22.0.0 up to, but not including, 22.2.10.12; 23.0.0 up to, but not including, 23.0.12.7; 24.0.0 up to, but not including, 24.0.12.2; 25.0.0 up to, but not including, 25.0.7; 26.0.0 up to, but not including, 26.0.219.0.13.9, 20.0.14.14, 21.0.9.12, 22.2.10.12, 23.0.12.7, 24.0.12.2

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
UnchangedImpact stays within the vulnerable component.
Confidentiality
NoneNo data is disclosed.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

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

Scoring systemScoreSeverityScored by
CVSS 3.17.6HighCNA (github.com)
CVSS 3.18.1HighNVD

Official description

NextCloud Server and NextCloud Enterprise Server provide file storage for Nextcloud, a self-hosted productivity platform. In NextCloud Server versions 25.0.0 until 25.0.7 and 26.0.0 until 26.0.2 and Nextcloud Enterprise Server versions 21.0.0 until 21.0.9.12, 22.0.0 until 22.2.10.12, 23.0.0 until 23.0.12.7, 24.0.0 until 24.0.12.2, 25.0.0 until 25.0.7, and 26.0.0 until 26.0.2, when two server are registered as trusted servers for each other and successfully exchanged the share secrets, the malicious server could modify or delete VCards in the system addressbook on the origin server. This would impact the available and shown information in certain places, such as the user search and avatar menu. If a manipulated user modifies their own data in the personal settings the entry is fixed again. Nextcloud Server n 25.0.7 and 26.0.2 and Nextcloud Enterprise Server 21.0.9.12, 22.2.10.12, 23.0.12.7, 24.0.12.2, 25.0.7, and 26.0.2 contain a patch for this issue. A workaround is available. Remove all trusted servers in the "Administration" > "Sharing" settings `…/index.php/settings/admin/sharing`. Afterwards, trigger a recreation of the local system addressbook with the following `occ dav:sync-system-addressbook`.

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: none, automatable: no, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Patches and release notes

Other references

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