# CVE-2026-53539: python-multipart: Python-Multipart is a streaming multipart parser for Python

CVE-2026-53539 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-53539, released June 22, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-53539
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0046
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 22, 2026

## Description

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. This vulnerability is fixed in 0.0.30.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | python-multipart Debian 14 | 0.0.32-1 | [DEBIAN-CVE-2026-53539](https://patchblox.com/security/data/fix/linux/debian-cve-2026-53539.md) | Jun 22, 2026 |
| Linux | python-python-multipart opensuse-leap 16.0 | 0.0.20-160000.5.1 | [OPENSUSE-SU-2026:21066-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21066-1.md) | Jun 26, 2026 |
| Linux | python-python-multipart sles 16.0 | 0.0.20-160000.5.1 | [SUSE-SU-2026:22372-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22372-1.md) | Jun 26, 2026 |

---

Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.