The vulnerability allows a block producer to set unused padding bits in the PubKeysBitmap field so that they count toward the BLS signature quorum. Because those padding bits do not correspond to any real validator, the aggregate‑signature verification still succeeds while the actual quorum of genuine validator signatures is lower than required. Nodes that accept such a header believe the block has a valid two‑thirds quorum, thereby weakening consensus safety and undermining finality.

Klever‑Go, the Go implementation of the Klever blockchain protocol. All releases before version 1.7.20 are vulnerable. Versions 1.7.20 and later have fixed the counting of padding bits.

The CVSS score of 7.1 indicates a high severity vulnerability with no known mitigations beyond the fix. The EPSS score is not available, and the vulnerability is not listed in CISA’s KEV catalog, but its impact on blockchain consensus makes it critical for operators. A malicious or compromised block producer can craft a header with padding bits that inflate the quorum, allowing them to overstate validator participation and potentially forge blocks. Verification of the padding bits is required to restore proper quorum enforcement.