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HIGH

CVE-2026-49855

CVSS v3

7.5

HIGH

EPSS Score

0.6 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • tornadoPyPIall versions · fixed in 6.5.6
  • python3-tornadoAlmaLinux:10all versions · fixed in 6.5.8-0.el10_2.1
  • python3-tornadoAlmaLinux:9all versions · fixed in 6.5.8-0.el9_8.1

Vendor advisories

  • CVE-2026-49855 Red Hat Product Security55 products fixed · 43 known affected

    tornado: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption

    exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 as a component of Exploit Intelligence · keylime as a component of Red Hat Enterprise Linux 10 · keylime-base as a component of Red Hat Enterprise Linux 10

  • RHSA-2026:84734 Red Hat Product Security14 products fixed

    Red Hat Security Advisory: RHOAI 3.4.5 - Red Hat OpenShift AI

  • RHSA-2026:80741 Red Hat Product Security13 products fixed

    Red Hat Security Advisory: python-tornado security update

  • RHSA-2026:73987 Red Hat Product Security2 products fixed

    Red Hat Security Advisory: RHOAI 3.3.7 - Red Hat OpenShift AI

  • RHSA-2026:67146 Red Hat Product Security13 products fixed

    Red Hat Security Advisory: python-tornado security update

  • RHSA-2026:67147 Red Hat Product Security13 products fixed

    Red Hat Security Advisory: python-tornado security update

Full record on NVD

Description

Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2026-07-14
Last Modified
2026-07-15

Frequently asked questions

What is CVE-2026-49855?

Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.

Is CVE-2026-49855 actively exploited?

Active exploitation of CVE-2026-49855 has not been confirmed. Its EPSS score was 0.6% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-49855?

CVE-2026-49855 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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