VulnerabilityPublished 4 Apr 2023Updated 3 Nov 2025

CVE-2023-28997: nextcloud security-advisories · Reusing a Nonce, Key Pair in Encryption

Affects nextcloud security-advisoriesSource CVE Database V5

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Not known to be exploited · CVSS 6.7 Medium : upgrade to 3.6.5 when convenient.

Data as of 2 Nov 2026, 10:57 UTC

CVSS 3.1 base score

6.7Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.0% chance of exploitation in 30 days – higher than 64% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.6.5

CVSS:3.1/AV:P/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:N

Attack Vector: Physical
Attack Complexity: Low
Privileges Required: High
User Interaction: Required
Scope: Changed
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Physical: The attack requires the attacker to physically touch or manipulate the vulnerable component. Physical interaction may be brief or persistent.
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Apr 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade nextcloud/desktop to 3.6.5.

Affected software

Product	Affected	Fixed in
GitHubnextcloud/desktop`pkg:github/nextcloud/desktop`Other threats	Affected >=3.0.0 <3.6.5	Fixed in 3.6.5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

The primary and only effective mitigation is to upgrade all Nextcloud Desktop Client installations to version 3.6.5 or later immediately. Organizations should implement an urgent patch management process to identify and update all affected clients. Additionally, organizations should audit server administrator activities and access controls to detect any suspicious behavior that could indicate exploitation attempts. Employing strict server access policies, multi-factor authentication for administrators, and monitoring for anomalous file modifications can reduce risk. Network segmentation and limiting server administrator privileges to only necessary functions can also help. Since no workarounds exist, educating users about the importance of updating the client and avoiding synchronization with untrusted servers is critical. Organizations should also review their incident response plans to address potential data integrity or confidentiality incidents related to this vulnerability.

Description

The Nextcloud Desktop Client is a tool to synchronize files from Nextcloud Server. Starting with version 3.0.0 and prior to version 3.6.5, a malicious server administrator can recover and modify the contents of end-to-end encrypted files. Users should upgrade the Nextcloud Desktop client to 3.6.5 to receive a patch. No known workarounds are available.

Impact

For European organizations, this vulnerability poses a significant risk to the confidentiality and integrity of sensitive data synchronized via Nextcloud Desktop Client. Organizations relying on Nextcloud for secure file sharing, including government agencies, financial institutions, healthcare providers, and enterprises handling personal or regulated data, could face data breaches or undetected data tampering if a server administrator is malicious or if the server is compromised. The ability to recover and modify encrypted files undermines trust in the end-to-end encryption model, potentially exposing personal data protected under GDPR and other privacy regulations. This could lead to regulatory penalties, reputational damage, and operational disruptions. The attack requires high privileges on the server side, so insider threats or compromised server environments are the primary concern. Since no workarounds exist, failure to upgrade clients leaves organizations vulnerable. The impact is heightened in environments where Nextcloud is used extensively for collaboration and file synchronization across distributed teams.

CWE-323Reusing a Nonce, Key Pair in Encryption (opens in a new tab)
Base weaknessLikelihood of exploit: HighOWASP Top 10 A04:2025: Cryptographic Failures (opens in a new tab)
Nonces should be used for the present occasion and only once.
Implementation
Refuse to reuse nonce values.
Implementation
Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.
OWASP Cheat Sheets
Forgot Password (opens in a new tab)
Transport Layer Protection (opens in a new tab)
User Privacy Protection (opens in a new tab)
Password Storage (opens in a new tab)
Cryptographic Storage (opens in a new tab)
OWASP ASVS 4.0.3
V2.3.1 (opens in a new tab)
V2.6.2 (opens in a new tab)
V2.7.6 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 3 Nov 2025, 18:49 UTC

WeaknessesCWE-323

Technical details

References

Community reviews

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