CVE-2019-15617Network attack vector

Account takeover via alternate second-factor enrollment

Published Feb 4, 2020 · Updated Aug 5, 2024

Improper authentication in Nextcloud Server 17.0.0 allows remote attackers to take over accounts through a second-factor bypass. During the two-factor login flow, the server lets a password-validated session enroll an alternate provider without first completing an already configured provider. The attacker needs a valid account password and an enabled, setup-capable alternate provider; successful enrollment bypasses the victim's configured factor.

CVSS severity5.4
Medium
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Nextcloud Server 17.0.0 allows remote attackers to take over accounts through a second-factor bypass. During the two-factor login flow, the server lets a password-validated session enroll an alternate provider without first completing an already configured provider. The attacker needs a valid account password and an enabled, setup-capable alternate provider; successful enrollment bypasses the victim's configured factor.

The record

CVE
CVE-2019-15617
Published
Feb 4, 2020
Updated
Aug 5, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Server
Classifications
CWE-287, T1078
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 4, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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=17.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Serverversion=17.0.1

Published CVSS scores

5.4NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
5.5NVDAV:N/AC:L/Au:S/C:P/I:P/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)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
T1078Valid Accounts

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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