The vulnerability lies in the netty incubator codec.ohttp library, where failure of HKDF_expand or EVP_HPKE_CTX_export silently produces a byte array filled with zeros. This zeroed key material is then used directly as the AEAD key for HTTP response encryption. Because the key is deterministic and attacker‑predictable, an adversary can potentially decrypt or forge encrypted responses, compromising the confidentiality and integrity of communications handled by applications that rely on this library. The weakness is a cryptographic key management flaw and is catalogued as CWE‑330.

netty:netty-incubator-codec-ohttp versions earlier than 0.0.21.Final are affected. The issue was fixed in 0.0.21.Final, which ensures that HKDF_expand and EVP_HPKE_CTX_export return non‑NULL key material on failure.

The CVSS score of 6.9 indicates moderate severity, and there is no EPSS score available, so the likelihood of exploitation is uncertain but not negligible. The vulnerability is not listed in CISA KEV. Attack directly against the library would require the attacker to influence the DP library, potentially by crafting input that triggers failure or by controlling the library build. If such injection or control is possible, the attacker could observe the use of a zero‑key and then exploit the weakened encryption for later traffic. Otherwise, the risk is limited to environments that fail silently, especially if no additional validation of key material exists.