CyberSecBulletin
CVE-2023-48239NVD status: Modified

security-advisories: Improper Access Control

Published Updated By the CyberSecBulletin desk

CVE-2023-48239 is a high-severity improper access control vulnerability in security-advisories from Nextcloud, with a CVSS 3.1 base score of 7.1 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: >= 25.0.0, < 25.0.13; >= 26.0.0, < 26.0.8; >= 27.0.0, < 27.1.3, 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 0.95% chance of exploitation within 30 days, higher than 62% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Nextcloud Server to 20.0.14.16 or 21.0.9.13 or 22.2.10.15 or 23.0.12.12, 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-advisories>= 25.0.0, < 25.0.13; >= 26.0.0, < 26.0.8; >= 27.0.0, < 27.1.3; >= 20.0.0, < 20.0.14.16; >= 21.0.0, < 21.0.9.13; >= 22.0.0, < 22.2.10.15; >= 23.0.0, < 23.0.12.12; >= 24.0.0, < 24.0.12.8Not stated
NextcloudNextcloud Server20.0.0 up to, but not including, 20.0.14.16; 21.0.0 up to, but not including, 21.0.9.13; 22.0.0 up to, but not including, 22.2.10.15; 23.0.0 up to, but not including, 23.0.12.12; 24.0.0 up to, but not including, 24.0.12.8; 25.0.0 up to, but not including, 25.0.13; 26.0.0 up to, but not including, 26.0.8; 27.0.0 up to, but not including, 27.1.320.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13

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
LowLimited modification of data is possible.
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:L/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.18.5HighCNA (github.com)
CVSS 3.17.1HighNVD

Official description

Nextcloud Server provides data storage for Nextcloud, an open source cloud platform. Starting in version 25.0.0 and prior to versions 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Server and starting in version 20.0.0 and prior to versions 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Enterprise Server, a malicious user could update any personal or global external storage, making them inaccessible for everyone else as well. Nextcloud Server 25.0.13, 26.0.8, and 27.1.3 and Nextcloud Enterprise Server is upgraded to 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 contain a patch for this issue. As a workaround, disable app files_external. This workaround 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: none, automatable: no, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Technical write-ups (may include proof of concept)

Other vulnerabilities in security-advisories

All security-advisories vulnerabilities

Recent Improper Access Control vulnerabilities

Spotted an error? Tell us.