CVE-2021-40346

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data tampering.

Exploit odds

58.8% chance of exploitation in the next 30 days (EPSS). Higher than most.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-09-08 17:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 04:06 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 58.8% in the next 30 days (EPSS).
• Severity: 7.5 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-09-08 17:15 UTC

Last modified

2026-06-17 04:06 UTC

Exploit probability

58.8% · EPSS, next 30 days

Weakness

CWE-190 · Integer overflow

Record status

Modified

Affected

• Haproxy < 2.0.25
• Haproxy < 2.2.17
• Haproxy < 2.3.14
• Haproxy < 2.4.4
• Haproxy 2.5
• Debian Linux 11.0
• Fedoraproject Fedora 33
• Fedoraproject Fedora 34

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-40346.md and follow it. Check whether this project is affected by CVE-2021-40346. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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