The netty incubator codec.bhttp is a java language binary http parser. Prior to version 0.0.21.Final, HKDF_expand returns non-NULL on failure. The byte[] is filled with zeros and has no way to distinguish success from failure. Since this output is used as HKDF key material for the response AEAD, a failure silently produces an all-zero key. When EVP_HPKE_CTX_export fails it also returns an empty byte[] array filled with zeros. This byte[] feeds directly into OHttpCrypto.createResponseAEAD(...). A silent all-zero export secret would produce a deterministic, attacker-predictable AEAD key. Version 0.0.21.Final patches the issue.
Exploitability
AV:NAC:LAT:NPR:NUI:NVulnerable System
VC:LVI:LVA:NSubsequent System
SC:NSI:NSA:N6.9/CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:NCryptography