CVE-2023-28999Public exploit

E2EE folder compromise via unverified metadata-key origin

Published Apr 4, 2023 · Updated Feb 11, 2025

Key-authentication failure in affected Nextcloud clients allows malicious server administrators to access E2EE folders. The clients accept attacker-chosen RSA-OAEP-encrypted metadata keys without authenticating their origin, then use the highest-index key to re-encrypt file metadata during synchronization. Control of the connected server data folder is required; successful key insertion exposes file contents and folder structure and permits files to be added.

CVSS severity6.9
Medium
EPSS probability0.68%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Key-authentication failure in affected Nextcloud clients allows malicious server administrators to access E2EE folders. The clients accept attacker-chosen RSA-OAEP-encrypted metadata keys without authenticating their origin, then use the highest-index key to re-encrypt file metadata during synchronization. Control of the connected server data folder is required; successful key insertion exposes file contents and folder structure and permits files to be added.

The record

CVE
CVE-2023-28999
Published
Apr 4, 2023
Updated
Feb 11, 2025
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-325, T1565.001
Attack vector
physical
Privileges
admin

Timeline

How it unfolded

  1. Apr 4, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 11, 2025Record 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=>= 3.0.0, < 3.8.0
  2. Affected versionversion=>= 3.0.5, < 4.8.0
  3. Affected versionversion=>= 3.13.0, < 3.25.0

What conditions does exploitation require?

Attack vectorphysical
Required privilegesadmin

What is affected?

Nextcloud GmbH · Security Advisoriesversion=>= 3.0.0, < 3.8.0; version=>= 3.0.5, < 4.8.0; version=>= 3.13.0, < 3.25.0

Published CVSS scores

6.9GitHub, Inc.CVSS:3.1/AV:P/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:L
6.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:L

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)
Vectorphysical
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-325Missing Cryptographic Step
T1565.001Stored Data Manipulation

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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