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CVE-2026-84378

CVE-2026-84378 · HTTPX2: Quadratic SSE line buffering can cause CPU denial of service

This page contains facts from public vulnerability sources. Check the original advisory before updating.

HTTPX2 is a next generation HTTP client for Python. From 2.5.0 until 2.10.0, the HTTPX2 Server-Sent Events parser in src/httpx2/httpx2/_sse.py repeatedly copies and rescans buffered text in _SSELineDecoder.decode() when an attacker-controlled or compromised SSE endpoint splits one unterminated line across many response chunks. The behavior affects httpx2.Client.sse() and httpx2.AsyncClient.sse(), and the total processing work grows quadratically with the line length, allowing a crafted stream to consume excessive CPU and block a synchronous worker or asynchronous event loop. This issue is fixed in version 2.10.0.

CVSS 5.9 · Medium · EPSS 0.3% · Fix available

Published
Updated

Stack: system · python

Affected products and versions

  • httpx2

    Versions
    • >= 2.5.0, < 2.10.0: Affected

    No fix published

  • python-httpx2 Debian:14

    Versions
    • 2.4.0-1
    • 2.5.0-1
    Affected ranges
    • ECOSYSTEM: < 2.12.0-1

    Update to 2.12.0-1

  • httpx2 PyPI

    Versions
    • 2.5.0
    • 2.6.0
    • 2.7.0
    • 2.8.0
    • 2.9.0
    • 2.9.1
    Affected ranges
    • ECOSYSTEM: ≥ 2.5.0, < 2.10.0

    Update to 2.10.0

  • python-httpx2 Ubuntu:26.10

    Versions
    • 2.5.0-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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