Vulnerability · Published Jun 22, 2026 · Assigned by GitHub_M
CVE-2026-53540Python-Multipart: Negative Content-Length in parse_form buffers the entire body in memory
Low 3.7
In plain English
A low-severity security flaw in python-multipart from Kludex. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 28% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.31, parse_form() did not validate the Content-Length header before using it to bound its chunked read of the request body. A negative Content-Length turned the bounded read into a read-until-EOF, so the entire body was loaded into memory in a single read instead of in fixed-size chunks. This vulnerability is fixed in 0.0.31.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | python-multipart | no fix listed | DEBIAN-CVE-2026-53540 |
| Debian:13 | python-multipart | no fix listed | DEBIAN-CVE-2026-53540 |
| Debian:14 | python-multipart | 0.0.32-1 | DEBIAN-CVE-2026-53540 |
| PyPI | python-multipart | 0.0.31 | PYSEC-2026-3040 |
| PyPI | python-multipart | 0.0.31 | GHSA-v9pg-7xvm-68hf |
| Ubuntu:25.10 | python-multipart | no fix listed | UBUNTU-CVE-2026-53540 |
| Ubuntu:26.04:LTS | python-multipart | no fix listed | UBUNTU-CVE-2026-53540 |
| Ubuntu:26.10 | python-multipart | no fix listed | UBUNTU-CVE-2026-53540 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Kludex | python-multipart | < 0.0.31 |
Weakness: CWE-1284 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L