CVE-2026-82407: Klever-Go Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9wh6-9hq7-9688",
  "modified" : "2026-09-23T21:24:08Z",
  "published" : "2026-09-23T21:24:08Z",
  "aliases" : [ "CVE-2026-82407" ],
  "summary" : "Klever-Go: Validator registration accepts an unvalidated BLS public key → consensus liveness DoS",
  "details" : "**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(...)`).\n\n### Description\n\nKlever 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.\n\nRuntime 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.\n\n### POC\n\nAttack: \n(1) stake the minimum to register a validator, submitting a 96-byte `BLSPublicKey` that is not a valid G2 point (arbitrary bytes). Registration succeeds. \n(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. \n\n\n\n### Impact\n\nEvery 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. \n\nRated **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.\n\n### Recommendation\n\nEnforce `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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/klever-io/klever-go"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.7.20"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.7.19"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/klever-io/klever-go/security/advisories/GHSA-9wh6-9hq7-9688"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/klever-io/klever-go/commit/11606a90ccc289f93d0175994733229b332d9cff"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/klever-io/klever-go/commit/642da967893884d635986fed3c43bdc679cbfe8f"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/klever-io/klever-go"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/klever-io/klever-go/releases/tag/v1.7.20"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-23T21:24:08Z",
    "nvd_published_at" : null
  }
}