Gose HmacShaCryptor.Hash flaw: constant MAC breaks JWE integrity
CVE-2026-89320 Published on October 23, 2026
HmacShaCryptor.Hash never hashes its input — returns constant HMAC_K("") for all inputs, voiding CBC-HMAC JWE integrity
`HmacShaCryptor.Hash` never hashed its input. For any input it returned `HMAC_K("")` the MAC of the empty message under the key. Every AES-CBC-HMAC JWE produced or verified by gose therefore carried an authentication tag that is constant per key and independent of the message, removing ciphertext integrity entirely.
Vulnerability Analysis
CVE-2026-89320 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. An automatable proof of concept (POC) exploit exists. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
Improper Validation of Integrity Check Value
The software does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission. Improper validation of checksums before use results in an unnecessary risk that can easily be mitigated. The protocol specification describes the algorithm used for calculating the checksum. It is then a simple matter of implementing the calculation and verifying that the calculated checksum and the received checksum match. Improper verification of the calculated checksum and the received checksum can lead to far greater consequences.
Affected Versions
Eclipse Foundation Eclipse KeyPont - GOSE:- Version 0.9.0, <= 0.13.0-rc1 is affected.
- Before 1.0.0-rc1 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.