CVE-2026-77633 Cloudreve: Storage-quota TOCTOU race allows quota bypass and storage-based denial of service
Authenticated users can bypass storage quotas via race conditions, exhausting host storage and denying service to other users.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77633?
CVE-2026-77633 is a high-severity vulnerability in cloudreve, published on 22 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-77633?
5 open source packages ship an affected version, including github.com/cloudreve/Cloudreve/v4, github.com/cloudreve/Cloudreve and github.com/cloudreve/Cloudreve/v3.
| Package | Affected | Fixed in |
|---|---|---|
github.com/cloudreve/Cloudreve/v4 Go | All versions | 4.0.0-20260715025621-7329602751c0 |
github.com/cloudreve/Cloudreve/v4 Go | All versions | 4.0.0-20260715025621-7329602751c0 |
github.com/cloudreve/Cloudreve/v4 Go | All versions | 4.0.0-20260715025621-7329602751c0 |
github.com/cloudreve/Cloudreve Go | All versions | None |
github.com/cloudreve/Cloudreve/v3 Go | All versions | None |
How do I fix CVE-2026-77633?
Upgrade github.com/cloudreve/Cloudreve/v4 to 4.0.0-20260715025621-7329602751c0 or later.
Is CVE-2026-77633 being exploited?
There is no known exploitation of CVE-2026-77633 in the wild and no public exploit code.
Sources
Also known as GHSA-xj3h-wwxq-gfcj, GO-2026-6578.