CVE-2025-67726: Tornado is a Python web framework and asynchronous networking library

Q: How do I fix CVE-2025-67726?

tornado: upgrade to 6.5.3. Exact commands for each OS are on this page.

Q: Is CVE-2025-67726 being exploited?

CVE-2025-67726 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-67726 affect?

CVE-2025-67726 affects tornado. Severity is high (CVSS 7.5). Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py

Q: How urgent is CVE-2025-67726?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2025-67726 is a high-severity flaw (CVSS 7.5) affecting tornado. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py is used to parse specific HTTP header values, such as those in multipart/form-data and repeatedly calls string.count() within a nested loop while processing quoted semicolons. If an attacker sends a request wit

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 55%)
CISA exploited list	No
Weakness	CWE-400, CWE-834
Published	2025-12-12
Last modified	2026-10-07

Publisher (CNA): GitHub, Inc. · Vendor: tornadoweb

Last updated 2026-10-07 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-12-12 07:15 UTCPublished CVE record published
2026-10-07 20:10 UTCUpdated Record last modified

tornadoweb tornado UPGRADE

Affected: < 6.5.3

Fixed in: 6.5.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy tornado || rpm -q tornado || tornado --version

2. UPGRADE to 6.5.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade tornado

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade tornado

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-67726?

tornado: upgrade to 6.5.3. Exact commands for each OS are on this page.

Is CVE-2025-67726 being exploited?

CVE-2025-67726 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-67726 affect?

CVE-2025-67726 affects tornado. Severity is high (CVSS 7.5). Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py

How urgent is CVE-2025-67726?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities

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References

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