GHSA-fw38-pc54-jvx9: Klever-Go KVM: Throttler slot leak in trie account-data sync causes epoch bootstrap / state sync DoS
SummaryThe account-data trie syncers leak bounded throttler slots on error paths in `syncDataTrie()`. Each failed trie sync permanently consumes one slot from
  the `NumGoRoutinesThrottler`, and the slot is never returned unless the sync succeeds or the root hash was already present.I confirmed this on the current default branch `develop` at commit `9640d63` (observed on May 20, 2026). I also confirmed the bug with a runtime PoC
  using the real timeout path in `trieSyncer.StartSyncing()`: two timed-out sync attempts are enough to exhaust a throttler with capacity `2`.This affects the epoch bootstrap path because `syncUserAccountsState()` and `syncKappAccountsState()` create bounded throttlers and abort bootstrap
  immediately if the syncer returns an error. Once enough trie-root sync attempts fail, the syncer cannot make forward progress and bootstrap fails.Affected Components`data/syncer/userAccountsSyncer.go``data/syncer/kappAccountsSyncer.go``data/trie/sync.go``core/throttler/numGoRoutinesThrottler.go``core/bootstrap/process.go`Affected VersionVerified on:`develop` HEAD `9640d63`Please check whether the same code is present in supported `1.7.x` releases.Suggested SeverityHighVulnerability DetailsRoot CauseBoth account-data syncers call `StartProcessing()` before creating / starting the trie syncer, but they only call `EndProcessing()` on the success path
  and on the duplicate-root early return.`userAccountsSyncer.syncDataTrie()`:Missing slot release pathsAfter StartProcessing(), the following error paths return without EndProcessing():trie.NewTrie(...) returns an errortrie.NewTrieSyncer(...) returns an errortrieSyncer.StartSyncing(...) returns an errorWhy this mattersNumGoRoutinesThrottler is a strict bounded counter:So after enough failures, further roots stop progressing and the sync operation eventually returns time is out.Bootstrap impactEpoch bootstrap uses these syncers directly and aborts on any error:The throttlers for these paths are real bounded throttlers created from numConcurrentTrieSyncers.Proof of ConceptI verified the bug with the real timeout path, not only with a canceled context.The PoC below uses:a real NumGoRoutinesThrottler with capacity 2a real trieSyncer.StartSyncing()an empty trie-node cache and a request handler that never supplies nodesa short sync timeout (1s) so StartSyncing() returns trie.ErrTimeIsOutAfter the first failed sync, one slot remains leaked.
  After the second failed sync, the throttler is exhausted.PoC testCommand usedResultThis confirms the leak with the real timeout path from trieSyncer.StartSyncing().ImpactAn attacker who can repeatedly cause trie-node sync failures or timeouts during bootstrap can consume the bounded sync throttler until no capacity
  remains.Once enough slots are leaked:additional account-data trie sync attempts stop making progressthe parent loop waits until context timeoutSyncAccounts() failsepoch bootstrap failsThis is a core node availability issue. It affects fresh/restarting nodes and validators that need to bootstrap or resync state.This is not a theoretical issue:StartSyncing() performs network-dependent trie-node retrievalit already has explicit timeout / failure pathsthe leaked throttler slots are confirmed by runtime PoCRecommended FixRelease the slot with defer immediately after StartProcessing() and cancel the defer only if ownership is intentionally transferred, which is not the
  case here.Example fix pattern:The same pattern should be applied to:data/syncer/userAccountsSyncer.godata/syncer/kappAccountsSyncer.goReferencesdata/syncer/userAccountsSyncer.godata/syncer/kappAccountsSyncer.godata/trie/sync.gocore/throttler/numGoRoutinesThrottler.gocore/bootstrap/process.goSECURITY.md
CVSS v3.1: 5.9