How severe is CVE-2026-31958?

No CVSS score has been assigned to CVE-2026-31958 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-31958?

CVE-2026-31958 affects the following packages: tornado (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-31958?

Update tornado to 6.5.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-31958 is resolved across your whole dependency graph.

How do I detect CVE-2026-31958 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tornado, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-31958 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-31958 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-31958 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-31958?

CVE-2026-31958 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 33th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-31958?

CVE-2026-31958 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-31958 published, and has it been updated?

CVE-2026-31958 was published on March 11, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-31958 — tornado

Fix: tornadoweb/tornado@119a195

CVE-2026-31958 is a Uncontrolled Resource Consumption vulnerability in tornado. A fix is available for tornado — see the affected versions and patch details below.

Tornado has a DoS due to too many multipart parts

Also known asGHSA-qjxf-f2mg-c6mcPYSEC-2026-140

Published

Mar 11, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 1, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-31958.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk-0.10%

Lower risk than most CVEs33th percentile — riskier than 33% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍tornado

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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.

Tornado 6.5.5 introduces new limits on the size and complexity of multipart bodies, including a default limit of 100 parts per request. These limits are configurable if needed; see tornado.httputil.ParseMultipartConfig. It is also now possible to disable multipart/form-data parsing entirely if it is not required for the application.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`tornado`	all versions	6.5.5`pip install --upgrade 'tornado==6.5.5'`

Affected Products

1 product · 1 configurations

Application

tornadotornadoweb

< 6.5.5

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tornado, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update tornado to 6.5.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-31958 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-31958 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Enterprise Linux 10	`python-tornado-0:6.5.5-1.el10_1.1`	RHSA-2026:13641
Red Hat Enterprise Linux 10	`python-tornado-0:6.5.5-1.el10_2`	RHSA-2026:19034
Red Hat Enterprise Linux 10.0 Extended Update Support	`python-tornado-0:6.4.2-1.el10_0.2`	RHSA-2026:20577
Red Hat Enterprise Linux 7 Extended Lifecycle Support	`python-tornado-0:4.2.1-5.el7_9.3`	RHSA-2026:24342
Red Hat Enterprise Linux 8	`pcs-0:0.10.18-2.el8_10.9`	RHSA-2026:8093
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support	`pcs-0:0.10.8-1.el8_4.11`	RHSA-2026:11493
Red Hat Enterprise Linux 8.6 Telecommunications Update Service	`pcs-0:0.10.12-6.el8_6.13`	RHSA-2026:11494
Red Hat Enterprise Linux 8.8 Telecommunications Update Service	`pcs-0:0.10.15-4.el8_8.11`	RHSA-2026:11495

UbuntuHIGH

USN-8198-1Ubuntu USN-8198-2Ubuntu

Frequently Asked Questions

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. Tornado 6.5.5 introduces new limits on the size and complexity of multipart bodies, including a default limit of 100 parts per request. These limits are configurable if needed; see `tornado.httputil.ParseMultipartConfig`. It is also now possible to disable `multipart/for

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