GHSA-75jv-vfxf-3865
MEDIUMAssemblyline 4 service client vulnerable to Arbitrary Write through path traversal in Client code
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.
Blast Radius
assemblyline-service-client🐍assemblyline-service-clientReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Path-Traversal -> Arbitrary File Write in Assemblyline Service Client
IMPORTANT: This vulnerability is valid if you decide to use the assemblyline-service-client outside of the normal practice to using Assemblyline in a production environment. In practice, this code should always be executed within a containerized environment such as assemblyline-v4-service which ensures filesystem-level permissions of what the running user is allowed to access. Furthermore, there is fewer chances for a MiTM compromise when deployed properly in a Docker or Kubernetes deployment where the platform will assign the correct network policies to secure connections between containers instead of relying on the user to set this up manually.
See https://github.com/CybercentreCanada/assemblyline/issues/382 for further discussion.
1. Summary
The Assemblyline 4 service client (task_handler.py) accepts a SHA-256 value returned by the service server and uses it directly as a local file name.
No validation / sanitisation is performed.
A malicious or compromised server (or any MITM that can speak to client) can return a path-traversal payload such as
../../../etc/cron.d/evil
and force the client to write the downloaded bytes to an arbitrary location on disk.
2. Affected Versions
| Item | Value |
|---|---|
| Component | assemblyline-service-client |
| Repository | CybercentreCanada/assemblyline-service-client |
| Affected | All releases up to master branch. |
3. CVSS 3.1 Vector & Score
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
4. Technical Details
| Field | Content |
|---|---|
| Location | assemblyline_service_client/task_handler.py, inside download_file() |
| Vulnerable Line | file_path = os.path.join(self.tasking_dir, sha256) |
| Root Cause | The sha256 string is taken directly from the service-server JSON response and used as a file name without any validation or sanitisation. |
| Exploit Flow | 1. Attacker (service server) returns HTTP 200 for GET /api/v1/file/../../../etc/cron.d/evil.<br>2. Client writes the response body to /etc/cron.d/evil.<br>3. Achieves arbitrary file write (code execution if file is executable). |
5. Impact
- Integrity – Overwrite any file writable by the service UID (often root).
- Availability – Corrupt critical files or exhaust disk space.
- Code Execution – Drop cron jobs, systemd units, or overwrite binaries.
6. Mitigation / Fix
import re
_SHA256_RE = re.compile(r'^[0-9a-fA-F]{64}\Z')
def download_file(self, sha256: str, sid: str) -> Optional[str]:
if not _SHA256_RE.fullmatch(sha256):
self.log.error(f"[{sid}] Invalid SHA256: {sha256}")
self.status = STATUSES.ERROR_FOUND
return None
# or your preferred way to check if a string is a shasum.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | assemblyline-service-client | all versions | 4.6.0.stable11 |
| 🐍PyPI | assemblyline-service-client | ≥ 4.6.1.dev0&&< 4.6.1.dev138 | 4.6.1.dev138 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for assemblyline-service-client. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update assemblyline-service-client to 4.6.0.stable11 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-75jv-vfxf-3865 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 pinpoints whether GHSA-75jv-vfxf-3865 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-75jv-vfxf-3865. 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-75jv-vfxf-3865 in your dependencies?
O3 detects GHSA-75jv-vfxf-3865 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.