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CVE-2026-116577

CVE-2026-116577 · Tornado: Quadratic CPU usage when parsing HTTP headers with line folding

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

Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.

CVSS 5.3 · Medium · EPSS 0.4% · Fix available

Published
Updated

Stack: system · python

Affected products and versions

  • tornado

    Versions
    • < 6.6: Affected

    No fix published

  • python-tornado Debian:12

    Versions
    • 6.2.0-3
    • 6.2.0-3+deb12u1
    • 6.2.0-3+deb12u2
    • 6.2.0-3+deb12u3
    • 6.2.0-3+deb12u4
    • 6.3.2-1
    • 6.4.0-1
    • 6.4.0-2
    • 6.4.1-1
    • 6.4.1-2
    • 6.4.1-3
    • 6.4.2-1
    • 6.4.2-2
    • 6.4.2-3
    • 6.5.2-1
    • 6.5.2-2
    • 6.5.2-3
    • 6.5.4-0.1
    • 6.5.4-1
    • 6.5.5-1
    • 6.5.5-2
    • 6.5.5-3
    • 6.5.5-4
    • 6.5.5-5
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Debian:13

    Versions
    • 6.4.2-3
    • 6.4.2-3+deb13u1
    • 6.4.2-3+deb13u2
    • 6.5.2-1
    • 6.5.2-2
    • 6.5.2-3
    • 6.5.4-0.1
    • 6.5.4-1
    • 6.5.5-1
    • 6.5.5-2
    • 6.5.5-3
    • 6.5.5-4
    • 6.5.5-5
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Debian:14

    Versions
    • 6.4.2-3
    • 6.5.2-1
    • 6.5.2-2
    • 6.5.2-3
    • 6.5.4-0.1
    • 6.5.4-1
    • 6.5.5-1
    • 6.5.5-2
    • 6.5.5-3
    • 6.5.5-4
    • 6.5.5-5
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • tornado PyPI

    Versions
    • 0.2
    • 1.0
    • 1.1
    • 1.1.1
    • 1.2
    • 1.2.1
    • 2.0
    • 2.1
    • 2.1.1
    • 2.2
    • 2.2.1
    • 2.3
    • 2.4
    • 2.4.1
    • 3.0
    • 3.0.1
    • 3.0.2
    • 3.1
    • 3.1.1
    • 3.2
    • 3.2.1
    • 3.2.2
    • 4.0
    • 4.0.1
    • 4.0.2
    • 4.1
    • 4.1b2
    • 4.2
    • 4.2.1
    • 4.2b1
    • 4.3
    • 4.3b1
    • 4.3b2
    • 4.4
    • 4.4.1
    • 4.4.2
    • 4.4.3
    • 4.4b1
    • 4.5
    • 4.5.1
    • 4.5.2
    • 4.5.3
    • 4.5b1
    • 4.5b2
    • 5.0
    • 5.0.1
    • 5.0.2
    • 5.0a1
    • 5.0b1
    • 5.1
    • 5.1.1
    • 5.1b1
    • 6.0
    • 6.0.1
    • 6.0.2
    • 6.0.3
    • 6.0.4
    • 6.0a1
    • 6.0b1
    • 6.1
    • 6.1b1
    • 6.1b2
    • 6.2
    • 6.2b1
    • 6.2b2
    • 6.3
    • 6.3.1
    • 6.3.2
    • 6.3.3
    • 6.3b1
    • 6.4
    • 6.4.1
    • 6.4.2
    • 6.4b1
    • 6.5
    • 6.5.1
    • 6.5.10
    • 6.5.2
    • 6.5.3
    • 6.5.4
    • 6.5.5
    • 6.5.6
    • 6.5.7
    • 6.5.8
    • 6.5.9
    • 6.5b1
    • 6.6a1
    • 6.6b1
    • 6.6rc1
    Affected ranges
    • ECOSYSTEM: < 6.6

    Update to 6.6

  • python-tornado Ubuntu:Pro:16.04:LTS

    Versions
    • 4.2.1-1ubuntu2
    • 4.2.1-1ubuntu3
    • 4.2.1-1ubuntu3.1
    • 4.2.1-1ubuntu3.1+esm1
    • 4.2.1-1ubuntu3.1+esm2
    • 4.2.1-1ubuntu3.1+esm3
    • 4.2.1-1ubuntu3.1+esm4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Ubuntu:Pro:18.04:LTS

    Versions
    • 4.5.1-2.1~build2
    • 4.5.2-1
    • 4.5.3-1
    • 4.5.3-1ubuntu0.1
    • 4.5.3-1ubuntu0.2
    • 4.5.3-1ubuntu0.2+esm1
    • 4.5.3-1ubuntu0.2+esm2
    • 4.5.3-1ubuntu0.2+esm3
    • 4.5.3-1ubuntu0.2+esm4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Ubuntu:Pro:20.04:LTS

    Versions
    • 5.1.1-4ubuntu1
    • 5.1.1-4ubuntu5
    • 6.0.3+really5.1.1-2
    • 6.0.3+really5.1.1-2build1
    • 6.0.3+really5.1.1-2build2
    • 6.0.3+really5.1.1-3
    • 6.0.3+really5.1.1-3ubuntu0.1~esm1
    • 6.0.3+really5.1.1-3ubuntu0.1~esm3
    • 6.0.3+really5.1.1-3ubuntu0.1~esm5
    • 6.0.3+really5.1.1-3ubuntu0.1~esm7
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Ubuntu:Pro:22.04:LTS

    Versions
    • 6.1.0-1build1
    • 6.1.0-2
    • 6.1.0-3
    • 6.1.0-3build1
    • 6.1.0-3ubuntu0.1~esm1
    • 6.1.0-3ubuntu0.1~esm2
    • 6.1.0-3ubuntu0.1~esm4
    • 6.1.0-3ubuntu0.1~esm5
    • 6.1.0-3ubuntu0.1~esm6
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Ubuntu:24.04:LTS

    Versions
    • 6.3.2-1
    • 6.4.0-0ubuntu1
    • 6.4.0-1
    • 6.4.0-1build1
    • 6.4.0-1ubuntu0.1
    • 6.4.0-1ubuntu0.2
    • 6.4.0-1ubuntu0.4
    • 6.4.0-1ubuntu0.5
    • 6.4.0-1ubuntu0.6
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Ubuntu:26.10

    Versions
    • 6.5.4-0.1
    • 6.5.5-2
    • 6.5.5-4
    • 6.5.5-5
    • 6.5.5-5ubuntu1.1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-tornado Ubuntu:26.04:LTS

    Versions
    • 6.4.2-3
    • 6.5.2-3
    • 6.5.4-0.1
    • 6.5.4-0.1ubuntu0.1
    • 6.5.4-0.1ubuntu0.2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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