Inconsistent interpretation of HTTP requests in Tornado - CVE-2023-54397
Published: August 12, 2023 / Updated: September 16, 2026
Vulnerability identifier: #VU128146
CSH Severity: Medium
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2023-54397
CWE-ID: CWE-444
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to perform HTTP request smuggling.
The vulnerability exists due to inconsistent interpretation of HTTP requests in tornado/http1connection.py when parsing Content-Length fields and chunk lengths containing non-standard characters. A remote attacker can send a specially crafted request to perform HTTP request smuggling.
Exploitation requires Tornado to be deployed behind certain proxies that interpret those non-standard characters differently.
Affected software
Tornado
Ubuntu
python3-tornado (Ubuntu package)
Ubuntu
python3-tornado (Ubuntu package)
How to mitigate CVE-2023-54397
Install security update from vendor's website.
Tornado - update to 6.3.3
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
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