Klever-Go: Validator registration accepts an unvalidated BLS public key → consensus liveness DoS

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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.

Source published

23 Sep 2026 19:17:59 UTC

Source modified

23 Sep 2026 19:42:17 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 4.0 · 7.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

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.

Source published

Sep 23, 2026, 7:17:59 PM (timezone not stated)

Source modified

Sep 23, 2026, 7:42:17 PM (timezone not stated)

Observed here

11 Nov 2026 16:11:05 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 7.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

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.

Source published

23 Sep 2026 20:17:16 UTC

Source modified

23 Sep 2026 20:17:16 UTC

Observed here

25 Oct 2026 16:19:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 7.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/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

**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.

Source published

23 Sep 2026 21:24:08 UTC

Source modified

1 Oct 2026 20:56:13 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

Publisher rating · HIGH

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

Source published

1 Oct 2026 20:23:38 UTC

Source modified

1 Oct 2026 20:45:15 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.