GHSA-3x6r-wxxg-53vv is a medium-severity (CVSS 5.3) CWE-248 vulnerability in github.com/rclone/rclone. A fix is available for github.com/rclone/rclone — see the affected versions and patch details below.
rclone: Infinite Scale TUS Creation Transport Error Causes a Nil-Response Panic
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-3x6r-wxxg-53vv.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-3x6r-wxxg-53vv plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/rclone/rcloneReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
1. Summary
A transport failure during the initial Infinite Scale TUS creation POST can return (nil response, non-nil error). Rclone dereferences the nil response before processing the error and panics. The production CreateUploader path reproduced the crash against a closed endpoint.
The security case is deployment-dependent. A one-shot upload already fails when its endpoint resets, while RC jobs recover panics in fs/rc/jobs/job.go and return a job error. The incremental denial of service is strongest in a long-lived VFS mount or concurrent/multi-remote CLI process where the upload runs in an unrecovered goroutine and the panic terminates unrelated work.
2. Affected Assets & Attack Surface
- Verified rclone revision:
a0c09f1381ae93e2a9a33c529d170186c61ad058(v1.74.0-240-ga0c09f138) - Current-master check:
backend/webdav/tus.gowas unchanged at master commit961266888fe797390c535386f3b3aa46f4853602on 2026-07-18 - Response evaluation:
backend/webdav/tus.go:45-59 - Creation path:
backend/webdav/tus.go:61-107 - Unrecovered VFS caller:
vfs/write.go:71-81 - Contained RC caller:
fs/rc/jobs/job.go:107-115 - Configuration: Infinite Scale WebDAV uploads using TUS
- Code triggers: any pre-response transport failure, including refusal, reset, timeout, DNS/TLS/proxy failure, or cancellation
- Security trigger: a malicious/compromised configured endpoint resets an upload in a long-lived or multi-workload process
3. Technical Root Cause Analysis
getTusLocationOrRetry switches on resp.StatusCode before checking whether resp is nil or handling the accompanying error. A nil response is valid when the HTTP transaction fails before a response is parsed. There is no recovery boundary in the WebDAV operation itself. Whether the panic is process-fatal depends on its caller: the VFS write path starts operations.Rcat in an unrecovered goroutine (vfs/write.go:71-81), whereas RC jobs wrap their function in recover (fs/rc/jobs/job.go:107-115).
4. Proof-of-Concept & Evidence
- Configure the actual Infinite Scale creation path to a closed local endpoint.
- Invoke
Object.CreateUploader. - The POST returns a transport error and no response.
getTusLocationOrRetrydereferencesresp.StatusCodeand panics.
A remote endpoint can produce the same (nil response, non-nil error) state by accepting and resetting the connection before returning an HTTP response. TLS prevents arbitrary response modification but does not prevent the configured endpoint from closing or resetting its own connection. Refusal, DNS, TLS, proxy, and cancellation failures exercise the code defect but do not by themselves identify a remote security actor.
5. Impact Assessment
In an unrecovered CLI or VFS upload goroutine, the panic terminates the rclone process and any unrelated work it hosts. A hostile configured endpoint can repeat the condition whenever the victim initiates a TUS upload. RC jobs are excluded from the process-wide impact because their execution boundary recovers the panic and records an error. In a one-shot process dedicated to the hostile endpoint, the incremental security impact over an ordinary transport error is limited.
6. Remediation Guidance
- Check
resp == nilbefore accessing response fields. - Pass transport errors through the existing retry policy and return a normal error after exhaustion.
- Test refusal, reset, timeout, DNS, TLS, proxy, and cancellation paths.
- Add panic containment to long-lived worker goroutines as defense in depth; keep nil handling as the primary fix.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/rclone/rclone | all versions | 1.75.0go get github.com/rclone/rclone@v1.75.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/rclone/rclone, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/rclone/rclone to 1.75.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3x6r-wxxg-53vv is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-3x6r-wxxg-53vv can be triaged on real exposure rather than presence alone.
Tailored to GHSA-3x6r-wxxg-53vv. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-3x6r-wxxg-53vv in your dependencies?
O3 Security finds GHSA-3x6r-wxxg-53vv across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.