CVE-2026-82407

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, core/kapp/validators/validators.go Register and the runtime validator update path accept a submitted BLSPublicKey without curve, prime-order subgroup, or nonzero validation. When a validator with a malformed key becomes eligible and is selected into a consensus group, MultiSigner.Reset and the corresponding signature verification creation path cannot deserialize the group key and cancel the slot. This causes repeated missed rounds and throughput degradation, and a network whose consensus group equals the eligible validator set can halt completely. Genesis validation is not affected because that path already performs CheckPublicKeyValid. This issue is fixed in version 1.7.20.

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, core/kapp/validators/validators.go Register and the runtime validator update path accept a submitted BLSPublicKey without curve, prime-order subgroup, or nonzero validation. When a validator with a malformed key becomes eligible and is selected into a consensus group, MultiSigner.Reset and the corresponding signature verification creation path cannot deserialize the group key and cancel the slot. This causes repeated missed rounds and throughput degradation, and a network whose consensus group equals the eligible validator set can halt completely. Genesis validation is not affected because that path already performs CheckPublicKeyValid. This issue is fixed in version 1.7.20.

Location: core/kapp/validators/validators.go:201 (Register), (genesis/checking/nodesSetupChecker.go:73). core/consensus/slot/bls/subslotStartSlot.go:165 core/consensus/.../headerSignatureVerify.go:123 (Create(...)).

Description

Klever uses a BDN (Boneh-Drijvers-Neven) BLS multi-signature over BLS12-381 to finalize blocks (crypto/signing/mcl/multisig/bls.go, herumi/bls-go-binary). The library is initialized with only bls.Init(bls.BLS12_381) and no order-verification flags, so Deserialize does not enforce prime-order-subgroup membership subgroup safety relies on explicit IsValidOrder() calls in the wrappers.

Runtime validator registration (validators.Register) stores the submitted 96-byte BLSPublicKey via SetBLSPublicKey with no curve check, no subgroup check, and no proof-of-possession (CreateValidatorContract carries the key but no signature proving key ownership; grep confirms no proofOfPossession/VerifyProof/BLSSignature verification anywhere in core/kapp/validators/). CheckPublicKeyValid — which does IsValid && IsValidOrder && !IsZero — runs only at genesis, not on runtime registration/update.

POC

Attack: (1) stake the minimum to register a validator, submitting a 96-byte BLSPublicKey that is not a valid G2 point (arbitrary bytes). Registration succeeds. (2) Once the validator is eligible and selected into a consensus group, every in-group node including the honest leader (group[0]) calls MultiSigner().Reset(groupPubKeys, selfIndex) at slot start, which deserializes all group keys via PublicKeyFromByteArray → herumi Deserialize deterministically fails on the malformed key → SetSlotCanceled(true). The verify side (Create(consensusPubKeys)) fails identically. No block is produced for that round.

Impact

Every consensus round whose group contains the malformed-key validator is a missed slot. One eligible bad-key validator poisons roughly a groupSize / eligibleSet fraction of rounds → sustained liveness degradation. Where the consensus group equals the eligible set (small or early-stage networks), this is a full chain halt. Cost is the minimum validator stake, permissionless, and repeatable; no fork flag gates the missing validation.

Rated High (Byzantine liveness; Critical on small validator sets). The severity scales down to a fractional missed-slot / throughput-degradation attack on a large validator set where the bad validator is only occasionally in the active group.

Recommendation

Enforce CheckPublicKeyValid (curve + prime-order subgroup + non-zero) on the submitted BLS key at runtime validator registration and config-update, and ideally require a proof-of-possession (a BLS signature over the validator's own key/identity) at registration to prove key ownership and well-formedness. Gate the stricter validation behind an epoch fork flag for reprocessing consistency.

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, core/kapp/validators/validators.go Register and the runtime validator update path accept a submitted BLSPublicKey without curve, prime-order subgroup, or nonzero validation. When a validator with a malformed key becomes eligible and is selected into a consensus group, MultiSigner.Reset and the corresponding signature verification creation path cannot deserialize the group key and cancel the slot. This causes repeated missed rounds and throughput degradation, and a network whose consensus group equals the eligible validator set can halt completely. Genesis validation is not affected because that path already performs CheckPublicKeyValid. This issue is fixed in version 1.7.20.

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, core/kapp/validators/validators.go Register and the runtime validator update path accept a submitted BLSPublicKey without curve, prime-order subgroup, or nonzero validation. When a validator with a malformed key becomes eligible and is selected into a consensus group, MultiSigner.Reset and the corresponding signature verification creation path cannot deserialize the group key and cancel the slot. This causes repeated missed rounds and throughput degradation, and a network whose consensus group equals the eligible validator set can halt completely. Genesis validation is not affected because that path already performs CheckPublicKeyValid. This issue is fixed in version 1.7.20.

Location: core/kapp/validators/validators.go:201 (Register), (genesis/checking/nodesSetupChecker.go:73). core/consensus/slot/bls/subslotStartSlot.go:165 core/consensus/.../headerSignatureVerify.go:123 (Create(...)).

Description

Klever uses a BDN (Boneh-Drijvers-Neven) BLS multi-signature over BLS12-381 to finalize blocks (crypto/signing/mcl/multisig/bls.go, herumi/bls-go-binary). The library is initialized with only bls.Init(bls.BLS12_381) and no order-verification flags, so Deserialize does not enforce prime-order-subgroup membership subgroup safety relies on explicit IsValidOrder() calls in the wrappers.

Runtime validator registration (validators.Register) stores the submitted 96-byte BLSPublicKey via SetBLSPublicKey with no curve check, no subgroup check, and no proof-of-possession (CreateValidatorContract carries the key but no signature proving key ownership; grep confirms no proofOfPossession/VerifyProof/BLSSignature verification anywhere in core/kapp/validators/). CheckPublicKeyValid — which does IsValid && IsValidOrder && !IsZero — runs only at genesis, not on runtime registration/update.

POC

Attack: (1) stake the minimum to register a validator, submitting a 96-byte BLSPublicKey that is not a valid G2 point (arbitrary bytes). Registration succeeds. (2) Once the validator is eligible and selected into a consensus group, every in-group node including the honest leader (group[0]) calls MultiSigner().Reset(groupPubKeys, selfIndex) at slot start, which deserializes all group keys via PublicKeyFromByteArray → herumi Deserialize deterministically fails on the malformed key → SetSlotCanceled(true). The verify side (Create(consensusPubKeys)) fails identically. No block is produced for that round.

Impact

Every consensus round whose group contains the malformed-key validator is a missed slot. One eligible bad-key validator poisons roughly a groupSize / eligibleSet fraction of rounds → sustained liveness degradation. Where the consensus group equals the eligible set (small or early-stage networks), this is a full chain halt. Cost is the minimum validator stake, permissionless, and repeatable; no fork flag gates the missing validation.

Rated High (Byzantine liveness; Critical on small validator sets). The severity scales down to a fractional missed-slot / throughput-degradation attack on a large validator set where the bad validator is only occasionally in the active group.

Recommendation

Enforce CheckPublicKeyValid (curve + prime-order subgroup + non-zero) on the submitted BLS key at runtime validator registration and config-update, and ideally require a proof-of-possession (a BLS signature over the validator's own key/identity) at registration to prove key ownership and well-formedness. Gate the stricter validation behind an epoch fork flag for reprocessing consistency.

Klever-Go: Validator registration accepts an unvalidated BLS public key → consensus liveness DoS in github.com/klever-io/klever-go