Python Library Tornado < 6.5.6 Multiple Vulnerabilities

high Nessus Plugin ID 321525

Synopsis

A Python library installed on the remote host is affected by multiple vulnerabilities.

Description

The version of the Tornado Python library installed on the remote host is prior to 6.5.6. It is, therefore, affected by multiple vulnerabilities:

- When SimpleAsyncHTTPClient follows a 3xx redirect, it shallow-copies the original HTTPRequest, rewrites the URL, decrements max_redirects, and removes only the Host header. It does not clear Authorization, auth_username, auth_password, or auth_mode when the redirect target changes origin. As a result, credentials intended for one origin can be forwarded to a different origin when follow_redirects=True, which is the default. (CVE-2026-49853)

- Tornado's gzip decompression routines work in limited-size chunks, but have no overall limit for the total size of decompressed chunks that they will accumulate (There has always been a limit for the total compressed size). This allows a malicious server to consume effectively unlimited amounts of memory if it is accessed via SimpleAsyncHTTPClient in its default configuration. (CVE-2026-49855)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Upgrade to Tornado version 6.5.6 or later.

Plugin Details

Severity: High

ID: 321525

File Name: python_tornado_6_5_6.nasl

Version: 1.1

Type: Local

Agent: windows, macosx, unix

Family: Misc.

Published: 6/19/2026

Updated: 6/19/2026

Configuration: Enable thorough checks (optional)

Supported Sensors: Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.4

CVSS v2

Risk Factor: High

Base Score: 7.8

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:C

CVSS Score Source: CVE-2026-49855

CVSS v3

Risk Factor: High

Base Score: 7.7

Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

CVSS Score Source: CVE-2026-49853

Vulnerability Information

CPE: cpe:/a:tornadoweb:tornado

Required KB Items: installed_sw/tornado

Patch Publication Date: 5/27/2026

Vulnerability Publication Date: 5/27/2026

Reference Information

CVE: CVE-2026-49853, CVE-2026-49855

IAVB: 2026-B-0166

Detections

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