Improper handling of highly compressed data in Tornado - CVE-2026-103262

Vulnerability identifier: #VU149941

CSH Severity: Medium

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-103262

CWE-ID: CWE-409

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to improper handling of highly compressed data in tornado.curl_httpclient.CurlAsyncHTTPClient when processing a gzip-compressed response from an attacker-controlled URL. A remote attacker can serve a decompression bomb to cause a denial of service.

The issue affects applications configured to use the curl HTTP client.

Tornado
Red Hat Enterprise Linux for IBM z Systems - Extended Update Support
Red Hat Enterprise Linux for Power, little endian - Extended Update Support
Red Hat Enterprise Linux for ARM 64 - Extended Update Support
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Ubuntu
Anolis OS
python3-tornado (Ubuntu package)
python3-tornado
python3-tornado-doc
python-tornado (Red Hat package)

Install security update from vendor's website.

Tornado - update to 6.5.9
python3-tornado (Ubuntu package) - addressed in versions 4.2.1-1ubuntu3.1+esm4, 4.5.3-1ubuntu0.2+esm4, 6.0.3+really5.1.1-3ubuntu0.1~esm7, 6.1.0-3ubuntu0.1~esm6, 6.4.0-1ubuntu0.6, 6.5.4-0.1ubuntu0.2, 6.5.5-5ubuntu1.1
python3-tornado - update to 6.5.6-2
python3-tornado-doc - update to 6.5.6-2
python-tornado (Red Hat package) - update to 6.5.10-0.el10_0.1

• https://github.com/tornadoweb/tornado/security/advisories/GHSA-chx6-46f5-w4vp

• Multiple vulnerabilities in Tornado
• Red Hat Enterprise Linux 10 update for python-tornado
• Ubuntu update for python-tornado
• Anolis OS update for python-tornado