CVE-2023-54397
Description
A flaw was found in Tornado's HTTP request header parsing logic. When processing incoming HTTP requests, Tornado fails to reject malformed Content-Length headers containing non-standard characters. An unauthenticated remote attacker can exploit this parsing discrepancy when Tornado is deployed behind a front-end proxy or load balancer to cause a request boundary mismatch. This allows the attacker to conduct HTTP request smuggling, bypass proxy-level security controls, and inject unauthorized requests directly into the backend application context.
Statement
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 discrepancy to bypass proxy-level security validation, leading to HTTP request smuggling, unauthorized backend access, or request hijacking.
Mitigation
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Changed | N/A | Changed |
| Confidentiality | Low | N/A | Low |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Non-Repudiation,Access Control
Technical Impact: Unexpected State; Hide Activities; Bypass Protection Mechanism
An attacker could create HTTP messages to exploit a number of weaknesses including 1) the message can trick the web server to associate a URL with another URL's webpage and caching the contents of the webpage (web cache poisoning attack), 2) the message can be structured to bypass the firewall protection mechanisms and gain unauthorized access to a web application, and 3) the message can invoke a script or a page that returns client credentials (similar to a Cross Site Scripting attack).
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