CVE-2025-43859

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.

Database specific

{
    "cna_assigner":  "GitHub_M",
    "cwe_ids":  [
        "CWE-444"
    ],
    "osv_generated_from":  "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/43xxx/CVE-2025-43859.json"
}

References

Affected packages

Git / github.com/python-hyper/h11

Affected ranges

Type

GIT

Repo

https://github.com/python-hyper/h11

Events

Introduced

Fixed

1c5b07581f058886c8bdd87adababd7d959dc7ca

Fixed

114803a29ce50116dc47951c690ad4892b1a36ed

Database specific

Show details

{
    "extracted_events":  [
        {
            "range":  [
                {
                    "introduced":  "0"
                },
                {
                    "fixed":  "0.16.0"
                }
            ],
            "source":  "AFFECTED_FIELD",
            "strategy":  "StringRangeExpression"
        },
        {
            "range":  [
                {
                    "fixed":  "114803a29ce50116dc47951c690ad4892b1a36ed"
                }
            ],
            "source":  "REFERENCES_COMMIT"
        }
    ]
}

Affected versions

v0.*

v0.11.0

v0.12.0

v0.13.0

v0.14.0

v0.15.0

v0.5.0

v0.6.0

v0.7.0

v0.8.0

v0.9.0

Database specific

source

"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2025-43859.json"