CVE-2023-28998Public exploit

E2EE folder compromise via default all-zero key

Published Apr 4, 2023 · Updated Feb 11, 2025

Missing cryptographic step in Nextcloud Desktop Client 3.0.0 through 3.6.4 allows attackers to read and alter E2EE files via server metadata. When a server returns an empty metadata-key map, the client accesses an absent map index and uses its default all-zero key to encrypt folder metadata. Control of the connected Nextcloud server and client synchronization are required; the server administrator can recover file keys, decrypt files, reconstruct names, and add files.

CVSS severity6.7
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

Missing cryptographic step in Nextcloud Desktop Client 3.0.0 through 3.6.4 allows attackers to read and alter E2EE files via server metadata. When a server returns an empty metadata-key map, the client accesses an absent map index and uses its default all-zero key to encrypt folder metadata. Control of the connected Nextcloud server and client synchronization are required; the server administrator can recover file keys, decrypt files, reconstruct names, and add files.

The record

CVE
CVE-2023-28998
Published
Apr 4, 2023
Updated
Feb 11, 2025
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-325, T1530, T1565.002
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

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 3.0.0, < 3.6.5

What conditions does exploitation require?

Attack vectorphysical
Required privilegesadmin

What is affected?

Nextcloud GmbH · Security Advisoriesversion=>= 3.0.0, < 3.6.5

Published CVSS scores

6.7GitHubCVSS:3.1/AV:P/AC:L/PR:H/UI:R/S:C/C:H/I:H/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.

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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
T1530Data from Cloud Storage
T1565.002Transmitted 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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