GHSA-8423-8fgw-73vq

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.

Database specific

{
    "cwe_ids": [
        "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-01T20:17:38Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
}

References

Affected packages

PyPI / tornado

Package

Name: tornado; View open source insights on deps.dev
Purl: pkg:pypi/tornado

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Fixed

6.5.8

Affected versions

0.*

0.2

1.*

1.0

1.1

1.1.1

1.2

1.2.1

2.*

2.0

2.1

2.1.1

2.2

2.2.1

2.3

2.4

2.4.1

3.*

3.0

3.0.1

3.0.2

3.1

3.1.1

3.2

3.2.1

3.2.2

4.*

4.0

4.0.1

4.0.2

4.1b2

4.1

4.2b1

4.2

4.2.1

4.3b1

4.3b2

4.3

4.4b1

4.4

4.4.1

4.4.2

4.4.3

4.5b1

4.5b2

4.5

4.5.1

4.5.2

4.5.3

5.*

5.0a1

5.0b1

5.0

5.0.1

5.0.2

5.1b1

5.1

5.1.1

6.*

6.0a1

6.0b1

6.0

6.0.1

6.0.2

6.0.3

6.0.4

6.1b1

6.1b2

6.1

6.2b1

6.2b2

6.2

6.3b1

6.3

6.3.1

6.3.2

6.3.3

6.4b1

6.4

6.4.1

6.4.2

6.5b1

6.5

6.5.1

6.5.2

6.5.3

6.5.4

6.5.5

6.5.6

6.5.7

Database specific

last_known_affected_version_range

"<= 6.5.7"

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-8423-8fgw-73vq/GHSA-8423-8fgw-73vq.json"