CVE-2026-33555
MEDIUM 5.8EPSS 0.6%
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
- HAProxy
- CVSS v3.1 NVD
- 5.8 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N - CVSS v3.1 MITRE
- 4.0 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N - EPSS
- 0.60% chance of exploitation in the next 30 days, 48th percentile
- Published
- 2026-04-13
- Updated
- 2026-04-22
Proof-of-concept exploits (1)
- r3verii/CVE-2026-335552★ · 2026-04-17
Security advisories
- https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html
- haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84
- https://www.haproxy.com/documentation/haproxy-aloha/changelog
- https://www.mail-archive.com/haproxy@formilux.org/msg46752.html
- https://www.haproxy.org