Resource exhaustion in Tornado - CVE-2026-91990

Vulnerability identifier: #VU149938

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-2026-91990

CWE-ID: CWE-400

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 uncontrolled resource consumption in the parse_multipart_form_data function in httputil.py when processing multipart/form-data requests. A remote attacker can send a multipart request containing numerous parts to cause a denial of service.

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
python3-tornado (Ubuntu package)
python-tornado (Red Hat package)

Install security update from vendor's website.

Tornado - update to 6.5.8
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
python-tornado (Red Hat package) - update to 6.5.8-0.el10_0.1

• https://github.com/tornadoweb/tornado/security/advisories/GHSA-8423-8fgw-73vq

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