medium4.0
CVE-2026-33555
An issue was discovered in HAProxy before 3.3.6.
Impact
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.
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Haproxy | Haproxy | from 2.6.0 before 3.3.6 |
Weakness classification
References
- NVD record
- CVE.org record
- 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
- https://lists.debian.org/debian-lts-announce/2026/10/msg00036.html