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PYSEC-2026-1435

Vulnerability from pysec - Published: 2026-07-07 16:03 - Updated: 2026-07-07 17:24
VLAI
Details

Summary

HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls.

Severity
6.9 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Impacted products
Name purl
h2 pkg:pypi/h2
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "h2",
        "purl": "pkg:pypi/h2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.1.0",
        "1.0.0",
        "1.1.0",
        "1.1.1",
        "2.0.0",
        "2.1.0",
        "2.1.1",
        "2.1.2",
        "2.1.3",
        "2.1.4",
        "2.1.5",
        "2.2.0",
        "2.2.1",
        "2.2.2",
        "2.2.3",
        "2.2.4",
        "2.2.5",
        "2.2.6",
        "2.2.7",
        "2.3.0",
        "2.3.1",
        "2.3.2",
        "2.3.3",
        "2.3.4",
        "2.4.0",
        "2.4.1",
        "2.4.2",
        "2.4.3",
        "2.4.4",
        "2.5.0",
        "2.5.1",
        "2.5.2",
        "2.5.3",
        "2.5.4",
        "2.6.0",
        "2.6.1",
        "2.6.2",
        "3.0.0",
        "3.0.1",
        "3.1.0",
        "3.1.1",
        "3.2.0",
        "4.0.0",
        "4.1.0",
        "4.2.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2025-57804",
    "GHSA-847f-9342-265h"
  ],
  "details": "### Summary\n\nHTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls.",
  "id": "PYSEC-2026-1435",
  "modified": "2026-07-07T17:24:17.277303Z",
  "published": "2026-07-07T16:03:01.951354Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-57804"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/python-hyper/h2"
    },
    {
      "type": "WEB",
      "url": "https://lists.debian.org/debian-lts-announce/2025/09/msg00004.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/h2"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-847f-9342-265h"
    }
  ],
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "h2 allows HTTP Request Smuggling due to illegal characters in headers"
}



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Nomenclature

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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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