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CVE-2026-77633— Cloudreve: Storage-quota TOCTOU race allows quota bypass and storage-based denial of service

Quick assessment

Affected
cloudreve cloudreve
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Cloudreve is a self-hosted file management and sharing system. Prior to 4.18.0, PrepareUpload in pkg/filemanager/fs/dbfs/upload.go checks a stale in-memory user storage value through validateUserCapacity and later applies an unconditional storage charge outsid

CVSS 7.1 · High

Affected Version Matrix 1

VendorProduct Version RangeStatus
cloudreve cloudreve < 4.18.0 affected
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I. Basic Information for CVE-2026-77633

Vulnerability Information

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Vulnerability Title
Cloudreve: Storage-quota TOCTOU race allows quota bypass and storage-based denial of service
Source: CVE Program / CVE List V5
Vulnerability Description
Cloudreve is a self-hosted file management and sharing system. Prior to 4.18.0, PrepareUpload in pkg/filemanager/fs/dbfs/upload.go checks a stale in-memory user storage value through validateUserCapacity and later applies an unconditional storage charge outside the same quota-enforcing transaction. An authenticated user with Files.Write permission can issue concurrent upload-session requests that read the same capacity snapshot, all pass the MaxStorage check, and reserve their declared sizes through CommitWithStorageDiff. The resulting reservations can exceed the account quota and can be materialized as chunked uploads that exhaust host storage and deny uploads to other users. The default local-storage policy and default User group are affected. This issue is fixed in version 4.18.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
使用共享资源的并发执行不恰当同步问题(竞争条件)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
cloudreve cloudreve < 4.18.0 -

II. Public POCs for CVE-2026-77633

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III. Intelligence Information for CVE-2026-77633

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Patches & Fixes for CVE-2026-77633 (1)

Other References for CVE-2026-77633 (2)

Same Patch Batch · cloudreve · 2026-09-22 · 3 CVEs total

CVE-2026-79913 6.5 MEDIUM Cloudreve: SSRF guard bypass: checkIP does not decode IPv6-transition wrappers (NAT64, IPv
CVE-2026-77637 3.8 LOW Cloudreve: Privilege Scope Bypass: State-Mutating Admin Operations Accessible via Read-Onl

IV. Related Vulnerabilities

Same product: cloudreve
Same vendor: cloudreve
Same weakness: CWE-362

V. Comments for CVE-2026-77633

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