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
- Oct 17, 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
Proof-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.
Proof-of-concept exploit for CVE-2021-40346, an integer overflow in HAProxy enabling HTTP request smuggling and potential access control bypass.
CVE-2021-40346 PoC (HAProxy HTTP Smuggling)
CVE-2021-40346 integer overflow enables http smuggling
HAProxy CVE-2021-40346
Responsible use
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