NVD / CVE Program· CNA GitHub_M

CVE-2026-31958: Tornado has a DoS due to too many multipart parts

Noroxi assessment

Priority: Monitor (action score 34/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.41% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: tornadoweb tornado 6.5.5.

Low priority for now. Upgrade to tornadoweb tornado 6.5.5 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Tornado is a Python web framework and asynchronous networking library. In versions of Tornado prior to 6.5.5, the only limit on the number of parts in multipart/form-data is the max_body_size setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. This vulnerability is fixed in 6.5.5.

HighCVSS 8.7 · v4.0—No exploit Fix available

Published: Mar 11, 2026
Updated: Jun 17, 2026
EPSS: 0.4% · 36th percentile
CWE: CWE-400

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 34 / 40 · 8.7 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 8.7; NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
tornadoweb	tornado	cpe:2.3:a:tornadoweb:tornado

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

tornadoweb tornadobefore 6.5.5

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

tornadoweb tornado
- < 6.5.5affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
AlmaLinux:10	python3-tornado	before 6.5.5-1.el10_1.1	6.5.5-1.el10_1.1
AlmaLinux:10	python3-tornado	before 6.5.5-1.el10_2	6.5.5-1.el10_2
AlmaLinux:8	pcs	before 0.10.18-2.el8_10.9.alma.1	0.10.18-2.el8_10.9.alma.1
AlmaLinux:8	pcs-snmp	before 0.10.18-2.el8_10.9.alma.1	0.10.18-2.el8_10.9.alma.1
AlmaLinux:9	python3-tornado	before 6.5.5-1.el9_8	6.5.5-1.el9_8
AlmaLinux:9	python3-tornado	before 6.5.5-1.el9_7.1	6.5.5-1.el9_7.1
Debian:12	python-tornado	from 0	—
Debian:14	python-tornado	before 6.5.5-1	6.5.5-1
openSUSE:Leap 15.6	python-tornado6	before 6.3.2-150400.9.15.1	6.3.2-150400.9.15.1
openSUSE:Leap 16.0	python-tornado6	before 6.5-160000.4.1	6.5-160000.4.1
openSUSE:Leap 16.0	salt	before 3006.0-160000.5.1	3006.0-160000.5.1
openSUSE:Leap 16.0	salt-test	before 3006.0-160000.5.1	3006.0-160000.5.1
openSUSE:Tumbleweed	python-tornado6	before 6.5.5-1.1	6.5.5-1.1
openSUSE:Tumbleweed	salt	before 3006.0-56.1	3006.0-56.1
PyPI	tornado	before 6.5.5	6.5.5
Red Hat:enterprise_linux_eus:10.0	python-tornado	before 0:6.4.2-1.el10_0.2	0:6.4.2-1.el10_0.2
Red Hat:enterprise_linux_eus:10.0	python-tornado-debugsource	before 0:6.4.2-1.el10_0.2	0:6.4.2-1.el10_0.2
Red Hat:enterprise_linux_eus:10.0	python3-tornado	before 0:6.4.2-1.el10_0.2	0:6.4.2-1.el10_0.2
Red Hat:enterprise_linux_eus:10.0	python3-tornado-debuginfo	before 0:6.4.2-1.el10_0.2	0:6.4.2-1.el10_0.2
Red Hat:enterprise_linux:10.1	python-tornado	before 0:6.5.5-1.el10_1.1	0:6.5.5-1.el10_1.1
Red Hat:enterprise_linux:10.1	python-tornado-debugsource	before 0:6.5.5-1.el10_1.1	0:6.5.5-1.el10_1.1
Red Hat:enterprise_linux:10.1	python3-tornado	before 0:6.5.5-1.el10_1.1	0:6.5.5-1.el10_1.1
Red Hat:enterprise_linux:10.1	python3-tornado-debuginfo	before 0:6.5.5-1.el10_1.1	0:6.5.5-1.el10_1.1
Red Hat:enterprise_linux:10.2	python-tornado	before 0:6.5.5-1.el10_2	0:6.5.5-1.el10_2

+76

Same product

tornadoweb: all records

Other highest-scoring records for the same primary product.

CVE-2024-14029Tornado before 6.4.1 HTTP Request Smuggling via Transfer-Encoding
36Monitor
CVE-2023-54397Tornado before 6.3.3 HTTP Request Smuggling via Content-Length
36Monitor
CVE-2026-103262Tornado before 6.5.9 Denial of Service via CurlAsyncHTTPClient
34Monitor

Published before and after this one in the same product

← EarlierCVE-2025-67725Dec 12, 2025 · Tornado is Vulnerable to Quadratic DoS via Repeated Header Coalescing
30Monitor
← EarlierCVE-2025-67726Dec 12, 2025 · Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
30Monitor
Later →CVE-2026-35536Apr 3, 2026 · In Tornado before 6.5.5, cookie attribute injection could occur because the domain, path, and samesite arguments to .RequestHandler.set_cook
21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
tornadoweb tornado	6.5.5 · description	Vendor (CNA)
almalinux:pcs	0.10.18-2.el8_10.9.alma.1 · AlmaLinux:8	Package registry (OSV)
almalinux:pcs-snmp	0.10.18-2.el8_10.9.alma.1 · AlmaLinux:8	Package registry (OSV)
almalinux:python3-tornado	6.5.5-1.el10_1.1 · AlmaLinux:10	Package registry (OSV)
debian:python-tornado	6.5.5-1 · Debian:14	Package registry (OSV)
opensuse:python-tornado6	6.3.2-150400.9.15.1 · openSUSE:Leap 15.6	Package registry (OSV)
opensuse:salt	3006.0-56.1 · openSUSE:Tumbleweed	Package registry (OSV)
opensuse:salt-test	3006.0-160000.5.1 · openSUSE:Leap 16.0	Package registry (OSV)
PyPI:tornado	6.5.5	Package registry (OSV)
red hat:pcs	0:0.11.1-10.el9_0.11 · Red Hat:rhel_e4s:9.0::highavailability	Package registry (OSV)
red hat:pcs-snmp	0:0.11.1-10.el9_0.11 · Red Hat:rhel_e4s:9.0::highavailability	Package registry (OSV)
red hat:python-tornado	0:6.5.5-1.el10_1.1 · Red Hat:enterprise_linux:10.1	Package registry (OSV)
red hat:python-tornado-debuginfo	0:4.2.1-5.el7_9.3 · Red Hat:rhel_els:7	Package registry (OSV)
red hat:python-tornado-debugsource	0:6.5.5-1.el10_1.1 · Red Hat:enterprise_linux:10.1	Package registry (OSV)
red hat:python-tornado-doc	0:4.2.1-5.el7_9.3 · Red Hat:rhel_els:7	Package registry (OSV)
red hat:python3-tornado	0:6.5.5-1.el10_1.1 · Red Hat:enterprise_linux:10.1	Package registry (OSV)
red hat:python3-tornado-debuginfo	0:6.5.5-1.el10_1.1 · Red Hat:enterprise_linux:10.1	Package registry (OSV)
rocky linux:pcs	0:0.10.18-2.el8_10.9 · Rocky Linux:8	Package registry (OSV)
rocky linux:python-tornado	0:6.5.5-1.el10_1.1 · Rocky Linux:10	Package registry (OSV)
suse:golang-github-lusitaniae-apache_exporter	1.0.10-90002.3.6.1 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:python-tornado	4.5.3-150000.3.19.1 · SUSE:Linux Enterprise Micro 5.3	Package registry (OSV)
suse:python-tornado6	6.3.2-150400.9.15.1 · SUSE:Linux Enterprise Module for Python 3 15 SP7	Package registry (OSV)
suse:saltbundlepy	3.11.13-90002.4.9.1 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:saltbundlepy-core	3.11.13-90002.4.9.1 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:saltbundlepy-m2crypto	0.45.1-90002.3.9.2 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:saltbundlepy-pyzmq	25.1.2-90002.3.9.1 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:saltbundlepy-simplejson	3.19.1-90002.3.6.1 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:saltbundlepy-tornado	6.3.2-90002.4.6.2 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:spacecmd	5.1.13-90002.3.9.1 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)
suse:uyuni-tools	5.1.26-90002.3.9.1 · SUSE:EL-9:Update:Products:MultiLinuxManagerTools:Update	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2025-6772589 days apartTornado is Vulnerable to Quadratic DoS via Repeated Header Coalescing
30Monitor
CVE-2025-6772689 days apartTornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
30Monitor
CVE-2026-82397173 days apartTornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop
30Monitor
CVE-2024-52804474 days apartTornado has HTTP cookie parsing DoS vulnerability
30Monitor
CVE-2026-115927229 days apartTornado: Event loop blocking and excess memory use from chunked bodies with many small chunks
21Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: X

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}