CVE-2026-33555

What it is

An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

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

Timeline

1. 2026-04-13 17:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-18 20:16 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.3% in the next 30 days (EPSS).
• Severity: 4.0 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-04-13 17:16 UTC

Last modified

2026-10-18 20:16 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-130

Record status

Modified

Affected

• Haproxy < 3.3.6

Attack profile CVSS 3.1 · 4.0

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

Low

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-2026-33555.md and follow it. Check whether this project is affected by CVE-2026-33555. 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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