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High, CVSS 7.1amended

Cloudreve: Storage-quota TOCTOU race allows quota bypass and storage-based denial of service

CVE-2026-77633GHSA-xj3h-wwxq-gfcj

What to do

Partial vendor fix. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Go github.com/cloudreve/Cloudreve/v3

    Affected
    every version
    Fixed in
    no fixed version recorded

  • Go github.com/cloudreve/Cloudreve

    Affected
    every version
    Fixed in
    no fixed version recorded

  • Go github.com/cloudreve/Cloudreve/v4

    Affected
    < 4.0.0-20260715025621-7329602751c0
    Fixed in
    4.0.0-20260715025621-7329602751c0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.1 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H
EPSS
  • CVE-2026-77633: 0.37% estimated exploitation activity in the next 30 days; percentile 30.77 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Cloudreve v4 splits the storage-quota check (reading the user's used bytes and comparing them to MaxStorage) and the charge (incrementing users.storage) into two non-atomic steps in the PrepareUpload code path. This creates a Time-of-Check to Time-of-Use (TOCTOU) race condition. Any authenticated user — including an unprivileged account in the default User group — can concurrently issue several upload-session requests that all read the same stale used snapshot, each pass the check, and then each contribute their declared size to users.storage. The end result is that the total approved capacity exceeds the group's MaxStorage many times over. The same primitive is trivially amplifiable into a storage-based denial of service. During PrepareUpload, Cloudreve reserves the declared size against users.storage before any bytes are written, so an attacker can push the reserved amount far beyond the host's physical disk (tested: a 1 GiB-quota account reserved 17 GiB in a single 20-way…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-xj3h-wwxq-gfcj

  2. Revision 2 · amended ·

    Amended from osv record GO-2026-6578

  3. Revision 1 · created ·

    Published from osv record GHSA-xj3h-wwxq-gfcj

Agent brief

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# Patch Next advisory brief: CVE-2026-77633

Advisory: Cloudreve: Storage-quota TOCTOU race allows quota bypass and storage-based denial of service
IDs: CVE-2026-77633, GHSA-xj3h-wwxq-gfcj
Record: https://patchnext.com/advisories/cve-2026-77633 (revision 3, source checked 26 Oct 2026, 15:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/cloudreve/Cloudreve/v4 4.0.0-20260715025621-7329602751c0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/cloudreve/Cloudreve/v3: affected every version
- Go github.com/cloudreve/Cloudreve: affected every version
- Go github.com/cloudreve/Cloudreve/v4: affected < 4.0.0-20260715025621-7329602751c0; fixed in 4.0.0-20260715025621-7329602751c0

## Suggested inspection (read-only)
- Go github.com/cloudreve/Cloudreve/v3: check the installed version with your package manager.
- Go github.com/cloudreve/Cloudreve: check the installed version with your package manager.
- Go github.com/cloudreve/Cloudreve/v4: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/cloudreve/Cloudreve/v3, github.com/cloudreve/Cloudreve, github.com/cloudreve/Cloudreve/v4.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GO-2026-6578 (OSV record GO-2026-6578 lists affected ranges: Go github.com/cloudreve/Cloudreve >=0; Go github.com/cloudreve/Cloudreve/v3 >=0; Go github.com/cloudreve/Cloudreve/v4 >=0 <4.0.0-20260715025621-7329602751c0 (fixed))
- Verified: https://osv.dev/vulnerability/GHSA-xj3h-wwxq-gfcj (OSV record GHSA-xj3h-wwxq-gfcj lists affected ranges: Go github.com/cloudreve/Cloudreve/v4 >=0 <4.0.0-20260715025621-7329602751c0 (fixed))
- Verified: https://github.com/advisories/GHSA-xj3h-wwxq-gfcj (GitHub-reviewed advisory GHSA-xj3h-wwxq-gfcj lists affected ranges: Go github.com/cloudreve/Cloudreve/v4 >=0 <4.0.0-20260715025621-7329602751c0)

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