CVE-2026-33555

Summary

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 Software

Weaknesses

• CWE-130: CWE-130 Improper Handling of Length Parameter Inconsistency

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: partial

Additional References

• https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html

References

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

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