Vulnerability Details 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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 21.5%
CVSS Severity
CVSS v3 Score 4.0
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
- https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html
Products affected by CVE-2026-33555
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cpe:2.3:a:haproxy:haproxy:2.6.0
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cpe:2.3:a:haproxy:haproxy:2.6.1
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cpe:2.3:a:haproxy:haproxy:2.6.15
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cpe:2.3:a:haproxy:haproxy:2.6.2
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cpe:2.3:a:haproxy:haproxy:2.6.23
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cpe:2.3:a:haproxy:haproxy:2.6.3
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cpe:2.3:a:haproxy:haproxy:2.6.4
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cpe:2.3:a:haproxy:haproxy:2.6.5
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cpe:2.3:a:haproxy:haproxy:2.6.6
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cpe:2.3:a:haproxy:haproxy:2.6.7
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cpe:2.3:a:haproxy:haproxy:2.6.8
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cpe:2.3:a:haproxy:haproxy:2.6.9
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cpe:2.3:a:haproxy:haproxy:2.7.0
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cpe:2.3:a:haproxy:haproxy:2.7.1
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cpe:2.3:a:haproxy:haproxy:2.7.10
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cpe:2.3:a:haproxy:haproxy:2.7.2
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cpe:2.3:a:haproxy:haproxy:2.7.3
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cpe:2.3:a:haproxy:haproxy:2.8.0
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cpe:2.3:a:haproxy:haproxy:2.8.16
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cpe:2.3:a:haproxy:haproxy:2.8.2
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cpe:2.3:a:haproxy:haproxy:2.9.0
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cpe:2.3:a:haproxy:haproxy:2.9.1
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cpe:2.3:a:haproxy:haproxy:2.9.10
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cpe:2.3:a:haproxy:haproxy:2.9.2
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cpe:2.3:a:haproxy:haproxy:2.9.3
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cpe:2.3:a:haproxy:haproxy:2.9.4
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cpe:2.3:a:haproxy:haproxy:2.9.5
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cpe:2.3:a:haproxy:haproxy:2.9.6
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cpe:2.3:a:haproxy:haproxy:2.9.7
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cpe:2.3:a:haproxy:haproxy:2.9.8
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cpe:2.3:a:haproxy:haproxy:2.9.9
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cpe:2.3:a:haproxy:haproxy:3.0.0
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cpe:2.3:a:haproxy:haproxy:3.0.1
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cpe:2.3:a:haproxy:haproxy:3.0.10
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cpe:2.3:a:haproxy:haproxy:3.0.11
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cpe:2.3:a:haproxy:haproxy:3.0.12
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cpe:2.3:a:haproxy:haproxy:3.0.13
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cpe:2.3:a:haproxy:haproxy:3.0.14
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cpe:2.3:a:haproxy:haproxy:3.0.15
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cpe:2.3:a:haproxy:haproxy:3.0.16
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cpe:2.3:a:haproxy:haproxy:3.0.17
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cpe:2.3:a:haproxy:haproxy:3.0.2
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cpe:2.3:a:haproxy:haproxy:3.0.3
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cpe:2.3:a:haproxy:haproxy:3.0.4
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cpe:2.3:a:haproxy:haproxy:3.0.5
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cpe:2.3:a:haproxy:haproxy:3.0.6
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cpe:2.3:a:haproxy:haproxy:3.0.7
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cpe:2.3:a:haproxy:haproxy:3.0.8
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cpe:2.3:a:haproxy:haproxy:3.0.9
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cpe:2.3:a:haproxy:haproxy:3.1
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cpe:2.3:a:haproxy:haproxy:3.2
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cpe:2.3:a:haproxy:haproxy:3.2.6
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cpe:2.3:a:haproxy:haproxy:3.3