EUVD-2026-54712Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Block producer role required (PR:L); consensus integrity fully undermined (I:H); no confidentiality or availability impact; network-delivered crafted header, low complexity once role is held.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
4DescriptionCVE.org
Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, header signature verification counts the unused padding bits of the PubKeysBitmap toward the two-thirds validator quorum. These padding bits do not correspond to any validator and are ignored by the actual BLS aggregate-signature check, so a malicious or compromised block producer can set them to reach the required quorum while gathering fewer genuine validator signatures than the protocol demands. As a result, nodes that import or intercept the header accept it as correctly signed without a real two-thirds quorum, weakening consensus safety and undermining finality. This issue is fixed in version 1.7.20.
AnalysisAI
Consensus quorum bypass in Klever-Go prior to v1.7.20 allows a low-privileged block producer to satisfy the two-thirds validator signature threshold using phantom padding bits in the PubKeysBitmap rather than genuine validator signatures. Because the BLS aggregate-signature check ignores bits beyond the consensus group size while the quorum counter does not, a crafted block header with set padding bits appears validly signed without a real supermajority, undermining blockchain finality and consensus safety. No public exploit has been identified at time of analysis; a vendor-released patch is available in version 1.7.20.
Technical ContextAI
Klever-Go implements BLS multisignature-based consensus in which a PubKeysBitmap byte array tracks which validators signed each block - one bit per validator. When the consensus group size is not a multiple of 8, the final byte of the bitmap contains trailing padding bits that map to no actual validator. The vulnerable code path in core/process/headerCheck/headerSignatureVerify.go (verifyConsensusSize) iterated over all set bits in the bitmap including these padding positions, counting them toward the two-thirds quorum threshold. The BLS aggregate verifier (blsMultisig.go AggregateSigs/Verify) correctly skips bits beyond numPubKeys, so these phantom bits pass cryptographic verification without a corresponding signature. This is a CWE-345 (Insufficient Verification of Data Authenticity) flaw: the quorum check fails to authenticate that counted bits represent real validators. Affected product per CPE: cpe:2.3:a:klever-io:klever-go:*:*:*:*:*:*:*:*.
RemediationAI
Upgrade Klever-Go to version 1.7.20 or later, which is confirmed by the vendor advisory at https://github.com/klever-io/klever-go/security/advisories/GHSA-f9h7-4mmq-vgcq. The patch (commit a11cb28e495e608d8034dbe83a91e89d0c68e0f7) adds explicit padding-bit rejection in both the header signature verifier (verifyConsensusSize) and the BLS multi-signer (AggregateSigs, Verify), returning ErrBitmapWithPaddingNotZero or ErrBitmapPaddingNotZero on any header whose bitmap has set bits beyond the consensus group size. For operators unable to upgrade immediately, restricting block producer eligibility to a tightly controlled and monitored validator set reduces the exploitable surface, though this is not a substitute for the patch. Anomaly detection on bitmap byte values - flagging headers where set bits exceed the declared consensus group size - may provide early warning of exploitation attempts.
Integer overflow in Klever-Go's semi-fungible token (SFT) add-quantity path prior to version 1.7.19 allows a mint-role h
Unbounded goroutine exhaustion in Klever-Go versions 1.7.14-1.7.17 allows any connected libp2p peer to remotely degrade
Unauthenticated remote crash in Klever-Go versions 1.7.14-1.7.17 allows any network peer to terminate a node process by
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External POC / Exploit Code
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