GHSA-8423-8fgw-73vq
Fix: tornadoweb/tornado#3704GHSA-8423-8fgw-73vq is a security vulnerability in tornado. O3 Security confirms whether GHSA-8423-8fgw-73vq is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
tornado: multipart split() creates huge temp list before max_parts check -> memory amplification DoS (httputil.py:34)
Real-World Exposure
tornadoReal-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
Description
Summary
parse_multipart_form_data (httputil.py:34) calls
data.split(b"--"+boundary+b"\r\n") before the max_parts check (:35).
A 600KB body with 100k parts creates a 100k-element transient list first,
then rejects transient memory amplification (each split element is a copy).
Pre-auth HTTP DoS.
Root cause
parts = data[:final_boundary_index].split(b"--" + boundary + b"\r\n") # :34 huge list first
if len(parts) > config.max_parts: # :35 check after
raise HTTPInputError("multipart/form-data has too many parts")
PoC
gist: https://gist.github.com/afldl/649861f25d39b53b7edbe0298e171617
poc.py + output.txt (100k parts from 600KB transient list).
Fix
Count separators without materializing the list (e.g. data.count(b"--"+boundary) first).
Credit
Reported by afldl, 2026-07.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | tornado | all versions | 6.5.8 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tornado. 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 tornado to 6.5.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8423-8fgw-73vq 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-8423-8fgw-73vq 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-8423-8fgw-73vq. 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-8423-8fgw-73vq in your dependencies?
O3 detects GHSA-8423-8fgw-73vq across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.