# 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. - **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 22 Sep 2026 - **Updated:** 25 Sep 2026 - **Also known as:** GHSA-xj3h-wwxq-gfcj, GO-2026-6578 ## 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. Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) ## 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 | Ecosystem | 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. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-77633 and fix it if it is affected. What it is: 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. Exploitation: There is no known exploitation of CVE-2026-77633 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/cloudreve/Cloudreve/v4 (Go): affected all versions; fixed in 4.0.0-20260715025621-7329602751c0 - github.com/cloudreve/Cloudreve/v4 (Go): affected all versions; fixed in 4.0.0-20260715025621-7329602751c0 - github.com/cloudreve/Cloudreve/v4 (Go): affected all versions; fixed in 4.0.0-20260715025621-7329602751c0 - github.com/cloudreve/Cloudreve (Go): affected all versions; no fix listed - github.com/cloudreve/Cloudreve/v3 (Go): affected all versions; no fix listed Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-77633/ (Markdown: https://insights.sbomify.com/CVE-2026-77633/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77633 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77633 - OSV: https://osv.dev/vulnerability/CVE-2026-77633 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-77633/ Summaries are generated and may contain mistakes; the official description above is the record.