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Nextcloud ServerApplication · Nextcloud

CVE-2026-45691

MEDIUM · 5.9 CVSS v3.1 Published 2026-06-01
Fix available
A fix is available. Upgrade to 29.0.16.16 / 30.0.17.9 or later.
See remediation →
65/100
Remediation priority · Elevated
Remotely reachable Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Nextcloud is an open source content collaboration platform. In Nextcloud Server from versions 32.0.0 to before 32.0.9, and 33.0.0 to before 33.0.3, a pre-2FA session cookie (created after successful password authentication but before TOTP completion) could be reused as a Bearer token to authenticate against DAV endpoints, granting read/write access and bypassing mandatory two-factor authentication. It is recommended that the Nextcloud Server is upgraded to 33.0.3 or 32.0.9. It is recommended that the Nextcloud Enterprise Server is upgraded to 33.0.3, 32.0.9, 31.0.14.5, 30.0.17.9 or 29.0.16.16

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-287

The mechanism that verifies who a user is can be side-stepped or fooled, letting an attacker act as someone they're not. Everything built on top of that identity then becomes untrustworthy. Fixing it means hardening the full authentication flow, including edge cases, tokens, and secondary paths.

General guidance for the improper authentication class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Nextcloud ServerApplication
Affected:>= 32.0.0, < 32.0.9>= 33.0.0, < 33.0.3>= 29.0.0, < 29.0.16.16>= 30.0.0, < 30.0.17.9>= 31.0.0, < 31.0.14.5

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
None

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 29.0.16.16 / 30.0.17.9 / 31.0.14.5 or later
Fixed in 29.0.16.1630.0.17.931.0.14.5
Vendor patch github.com →
Recommended fix High confidence

Upgrade to 33.0.3, 32.0.9, 30.0.17.9, or 29.0.16.16 depending on your current major version branch

  1. 1. Create a full backup of the Nextcloud instance (database, config, and data directories)
  2. 2. Put the Nextcloud server into maintenance mode
  3. 3. Use the package manager or occ upgrade command to upgrade to the appropriate fixed version based on your current major version
  4. 4. If upgrading across major versions (e.g., 29 to 32), upgrade incrementally through each major version following Nextcloud's documentation
  5. 5. Run occ maintenance:mode --off to disable maintenance mode
  6. 6. Verify the upgrade was successful by logging in and checking the version in Settings > Administration > Overview
  7. 7. Test DAV endpoint authentication to confirm the vulnerability is remediated
Caveat Major version upgrades may require database migrations and could have breaking changes; review Nextcloud's changelog before upgrading across major versions

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-45691 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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