GHSA-xhf4-832v-7xcr is a medium-severity (CVSS 5.9) Uncontrolled Resource Consumption vulnerability in github.com/rclone/rclone. A fix is available for github.com/rclone/rclone — see the affected versions and patch details below.
rclone: Unbounded HTTP CONNECT Response Headers Can Exhaust rclone Memory
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-xhf4-832v-7xcr.
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-xhf4-832v-7xcr 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
The shared HTTP CONNECT helper parses a proxy response with http.ReadResponse over an unrestricted buffered reader. The production helper accepted a valid response containing a 2 MiB header in three consecutive runs. A malicious or compromised configured proxy, or an active on-path actor controlling a plaintext HTTP-proxy hop, can grow memory until the process fails.
The security impact is process-wide exhaustion, not loss of access through the malicious proxy, which the proxy already controls. The victim must configure and use the proxy, so UI is Required and the rating is Medium.
2. Affected Assets & Attack Surface
- Verified rclone revision:
a0c09f1381ae93e2a9a33c529d170186c61ad058(v1.74.0-240-ga0c09f138) - Current-master check:
lib/proxy/http.gowas unchanged at master commit961266888fe797390c535386f3b3aa46f4853602on 2026-07-18 - Shared helper:
lib/proxy/http.go:23-81 - SFTP use:
backend/sftp/ssh_internal.go:25-45 - FTP use:
backend/ftp/ftp.go:465-479 - Proxy peer: configured malicious/compromised proxy or active on-path actor for a plaintext HTTP proxy
- TLS boundary: HTTPS proxy connections authenticate the proxy before this response is parsed, so an on-path actor must also defeat TLS
3. Technical Root Cause Analysis
HTTPConnectDial invokes http.ReadResponse(br, req) directly. This call does not inherit http.Transport.MaxResponseHeaderBytes. In the Go implementation used for validation, exported textproto.Reader.ReadMIMEHeader passes math.MaxInt64 limits, and textproto.NewReader explicitly instructs callers to use io.LimitReader or an equivalent bound for denial-of-service resistance. Rclone supplies no bound or total CONNECT-handshake deadline. The helper additionally returns the raw connection, so a safe remediation must preserve any tunnel bytes already buffered after the CONNECT response.
4. Proof-of-Concept & Evidence
- Configure the helper to use a test proxy.
- Accept rclone's CONNECT request.
- Return
HTTP/1.1 200 Connection Establishedwith anX-Fillheader containing 2 MiB of data. - The actual helper parses and accepts the entire response without a fixed ceiling; this succeeded in all three reruns.
The test establishes unbounded parsing behavior without intentionally exhausting the host.
5. Impact Assessment
Large or concurrent CONNECT responses can terminate the rclone process and interrupt unrelated FTP/SFTP remotes and mounts. Runtime OOM cannot be contained by RC panic recovery. SFTP reaches this parser before SSH server authentication, so target host-key validation does not constrain a malicious proxy; HTTPS proxy authentication does constrain ordinary on-path attackers.
6. Remediation Guidance
- Enforce a total CONNECT status/header budget before parsing.
- Add a fixed total handshake deadline as well as idle deadlines.
- Close the connection on an oversized or malformed response.
- Return a wrapper that consumes already buffered post-response tunnel bytes before the raw connection.
- Test large single/multiple headers, slow streaming, and concurrent handshakes.
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-xhf4-832v-7xcr 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-xhf4-832v-7xcr can be triaged on real exposure rather than presence alone.
Tailored to GHSA-xhf4-832v-7xcr. 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-xhf4-832v-7xcr in your dependencies?
O3 Security finds GHSA-xhf4-832v-7xcr across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.