CVE-2021-40346
An integer overflow exists in HAProxy 2.0 through 2.5 in htx_add_header that can be exploited to perform an HTTP request smuggling attack, allowing an...
- Published
- Sep 8, 2021
- Updated
- Aug 4, 2024
- Assigning CNA
- mitre
- Evidence observed
- Aug 8, 2026
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NHigh · next 30 days
- Percentile
- 99.1%
- Model date
- Sep 21, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
An integer overflow exists in HAProxy 2.0 through 2.5 in htx_add_header that can be exploited to perform an HTTP request smuggling attack, allowing an attacker to bypass all configured http-request HAProxy ACLs and possibly other ACLs.
Sources
7Proof-of-concept for CVE-2021-40346, demonstrating HTTP request smuggling in HAProxy via integer overflow, with Docker-based environment to bypass access controls.
HTTP Request Smuggling
PoC exploit for CVE-2021-40346: HAProxy integer overflow enabling HTTP request smuggling and ACL bypass. Includes analysis, reproduction steps, and mitigation guidance.
Responsible use
Use vulnerability information only on systems you own or are authorized to test. Kitploit links to public research metadata and does not store exploit code or malicious payloads.