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.
01
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-33555US | medium5.8 | Exploit | ||
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 clo… | ||||
02
references
External citations — patches, advisories, analysis.
- https://github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84FIX
- https://lists.debian.org/debian-lts-announce/2026/10/msg00036.htmlWEB
- https://nvd.nist.gov/vuln/detail/CVE-2026-33555WEB
- https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.htmlADVISORY
- https://www.haproxy.com/documentation/haproxy-aloha/changelog/ARTICLE
- https://www.haproxy.orgWEB
- https://www.mail-archive.com/haproxy@formilux.org/msg46752.htmlARTICLE
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