CVE-2026-53540: python-multipart: Negative Content-Length in parse_form buffers the entire body in memory

June 15, 2026

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.

References

github.com/Kludex/python-multipart/security/advisories/GHSA-v9pg-7xvm-68hf
github.com/advisories/GHSA-v9pg-7xvm-68hf
nvd.nist.gov/vuln/detail/CVE-2026-53540

Code Behaviors & Features

Detect and mitigate CVE-2026-53540 with GitLab Dependency Scanning

Secure your software supply chain by verifying that all open source dependencies used in your projects contain no disclosed vulnerabilities. Dependency Scanning using SBOM also detects vulnerabilities from proprietary advisories that this site does not include. Learn more about Dependency Scanning using SBOM →