{"cve":"CVE-2025-43859","nvd":{"published":"2025-04-24T19:15:47.060","modified":"2026-06-17T09:24:39.580","status":"Deferred","description":"h11 is a Python implementation of HTTP/1.1. Prior to version 0.16.0, a leniency in h11's parsing of line terminators in chunked-coding message bodies can lead to request smuggling vulnerabilities under certain conditions. This issue has been patched in version 0.16.0. Since exploitation requires the combination of buggy h11 with a buggy (reverse) proxy, fixing either component is sufficient to mitigate this issue.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","score":9.1},"cwes":["CWE-444"],"references":["https://github.com/python-hyper/h11/commit/114803a29ce50116dc47951c690ad4892b1a36ed","https://github.com/python-hyper/h11/security/advisories/GHSA-vqfr-h8mv-ghfj"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:01:11.054312287+00:00"},"epss":{"cve":"CVE-2025-43859","score":0.00594,"percentile":0.48419,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-vqfr-h8mv-ghfj","url":"https://osv.dev/vulnerability/GHSA-vqfr-h8mv-ghfj","summary":"h11 accepts some malformed Chunked-Encoding bodies","modified":"2026-10-27T16:45:03.535584040Z","packages":[{"ecosystem":"PyPI","name":"h11","purl":"pkg:pypi/h11","ranges":["<0.16.0"],"fixed":["0.16.0"]}]},{"id":"PYSEC-2026-348","url":"https://osv.dev/vulnerability/PYSEC-2026-348","summary":"h11 accepts some malformed Chunked-Encoding bodies","modified":"2026-07-01T20:22:54.082067Z","packages":[{"ecosystem":"PyPI","name":"h11","purl":"pkg:pypi/h11","ranges":["<0.16.0"],"fixed":["0.16.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}