CVE-2026-45278Network attack vector

Open redirect via protocol-relative login URL bypass

Published Jun 1, 2026 · Updated Jun 1, 2026

Open redirect in Nextcloud User OIDC 6.1.0 through 8.2.1 allows remote attackers to redirect users via a crafted login link. LoginController::getRedirectResponse strips only HTTP or HTTPS scheme-and-host prefixes, so a protocol-relative URL beginning with two slashes remains an external destination. The victim must follow the attacker-controlled link and complete an OIDC login; the resulting browser redirect sends the victim to an attacker-selected website.

CVSS severity6.1
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Open redirect in Nextcloud User OIDC 6.1.0 through 8.2.1 allows remote attackers to redirect users via a crafted login link. LoginController::getRedirectResponse strips only HTTP or HTTPS scheme-and-host prefixes, so a protocol-relative URL beginning with two slashes remains an external destination. The victim must follow the attacker-controlled link and complete an OIDC login; the resulting browser redirect sends the victim to an attacker-selected website.

The record

CVE
CVE-2026-45278
Published
Jun 1, 2026
Updated
Jun 1, 2026
Vendor
Nextcloud GmbH
Product
Nextcloud Security Advisories
Classifications
CWE-601, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 1, 2026Record 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=>= 6.1.0, < 8.2.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Security Advisoriesversion=>= 6.1.0, < 8.2.2

Published CVSS scores

3.3GitHub, Inc.CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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-601URL Redirection to Untrusted Site ('Open Redirect')
T1204.001Malicious Link

Public exploit references

No public exploit references are available in this record.

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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