CVE-2026-33555

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.

CVSS 3.1

5.8CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

EPSS

0.3% chance of exploitation in the next 30 days; higher than 23% of CVEs (scores of 2026-10-25)

CWE

CWE-130

Published

2026-04-13

Modified

2026-10-18

Record from

the NVD, synced 2026-10-19

Affected

• haproxy:haproxy

References

• https://github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84
• https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html
• https://www.haproxy.com/documentation/haproxy-aloha/changelog/
• https://www.haproxy.org
• https://www.mail-archive.com/haproxy@formilux.org/msg46752.html

Check your stackJSON