CVE-2023-39958Network attack vector

OAuth client secret brute force via unthrottled failures

Published Aug 10, 2023 · Updated Oct 10, 2024

Insufficient brute-force protection in Nextcloud Server allows remote attackers to brute-force configured OAuth2 client secrets. The public OauthApiController getToken endpoint compares submitted client credentials and returned failures without invoking response throttling. No authentication or user interaction is required, but a configured OAuth2 client and an associated authorization or refresh-token code are needed to reach the secret comparison.

CVSS severity5.8
Medium
EPSS probability0.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficient brute-force protection in Nextcloud Server allows remote attackers to brute-force configured OAuth2 client secrets. The public OauthApiController getToken endpoint compares submitted client credentials and returned failures without invoking response throttling. No authentication or user interaction is required, but a configured OAuth2 client and an associated authorization or refresh-token code are needed to reach the secret comparison.

The record

CVE
CVE-2023-39958
Published
Aug 10, 2023
Updated
Oct 10, 2024
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-307, T1110
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 10, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 10, 2024Record 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=>= 22.0.0, < 22.2.10.13
  2. Affected versionversion=>= 23.0.0, < 23.0.12.8
  3. Affected versionversion=>= 24.0.0, < 24.0.12.5
  4. Affected versionversion=>= 25.0.0, < 25.0.9
  5. Affected versionversion=>= 26.0.0, < 26.0.4
  6. Affected versionversion=>= 27.0.0, < 27.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Nextcloud GmbH · Security Advisoriesversion=>= 22.0.0, < 22.2.10.13; version=>= 23.0.0, < 23.0.12.8; version=>= 24.0.0, < 24.0.12.5; version=>= 25.0.0, < 25.0.9; version=>= 26.0.0, < 26.0.4; version=>= 27.0.0, < 27.0.1

Published CVSS scores

5.8GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
5.3NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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.

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-307Improper Restriction of Excessive Authentication Attempts
T1110Brute Force

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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