How severe is CVE-2023-54397?

No CVSS score has been assigned to CVE-2023-54397 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2023-54397?

CVE-2023-54397 affects the following packages: tornado (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2023-54397?

Update tornado to 6.3.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-54397 is resolved across your whole dependency graph.

How do I detect CVE-2023-54397 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-2023-54397 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2023-54397 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-54397 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-2023-54397?

CVE-2023-54397 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 32th 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-2023-54397?

CVE-2023-54397 is classified as CWE-444 (CWE-444). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-54397 published, and has it been updated?

CVE-2023-54397 was published on September 15, 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-2023-54397 — tornado

Fix: tornadoweb/tornado@b7a5dd2

CVE-2023-54397 is a CWE-444 vulnerability in tornado. A fix is available for tornado — see the affected versions and patch details below.

Tornado before 6.3.3 HTTP Request Smuggling via Content-Length

Also known asGHSA-qppv-j76h-2rpx

Published

Sep 15, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

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-2023-54397.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs32th percentile — riskier than 32% 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

Summary

Tornado interprets -, +, and _ in chunk length and Content-Length values, which are not allowed by the HTTP RFCs. This can result in request smuggling when Tornado is deployed behind certain proxies that interpret those non-standard characters differently. This is known to apply to older versions of haproxy, although the current release is not affected.

Details

Tornado uses the int constructor to parse the values of Content-Length headers and chunk lengths in the following locations:

`tornado/http1connection.py:445`

            self._expected_content_remaining = int(headers["Content-Length"])

`tornado/http1connection.py:621`

                content_length = int(headers["Content-Length"])  # type: Optional[int]

`tornado/http1connection.py:671`

            chunk_len = int(chunk_len_str.strip(), 16)

Because int("0_0") == int("+0") == int("-0") == int("0"), using the int constructor to parse and validate strings that should contain only ASCII digits is not a good strategy.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`tornado`	all versions	6.3.3`pip install --upgrade 'tornado==6.3.3'`

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 6.3.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-54397 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

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 HatCritical

A vulnerability was found in Tornado's HTTP header parsing logic. When deployed behind a front-end reverse proxy or load balancer, Tornado improperly accepts non-standard characters in Content-Length headers instead of rejecting the malformed request. An unauthenticated remote attacker can exploit this parsing…

Workaround published by Red Hat

Configure upstream reverse proxies or load balancers to strictly normalize or sanitize HTTP headers and reject malformed Content-Length headers before requests reach the Tornado application layer.

Source: Red Hat security advisory for CVE-2023-54397 (CC BY 4.0)

Frequently Asked Questions

## Summary Tornado interprets `-`, `+`, and `_` in chunk length and `Content-Length` values, which are not allowed by the HTTP RFCs. This can result in request smuggling when Tornado is deployed behind certain proxies that interpret those non-standard characters differently. This is known to apply to older versions of haproxy, although the current release is not affected. ## Details Tornado uses the `int` constructor to parse the values of `Content-Length` headers and chunk lengths in the following locations: ### `tornado/http1connection.py:445` ```python3 self._expected_content_r

O3 Security · Impact-Aware SCA

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