CVE-2021-21271 (Go, published 2021-01-26T21:15Z)
Description: value: Tendermint Core is an open source Byzantine Fault Tolerant (BFT) middleware that takes a state transition machine - written in any programming language - and securely replicates it on many machines. Tendermint Core v0.34.0 introduced a new way of handling evidence of misbehavior. As part of this, we added a new Timestamp field to Evidence structs. This timestamp would be calculated using the same algorithm that is used when a block is created and proposed. (This algorithm relies on the timestamp of the last commit from this specific block.) In Tendermint Core v0.34.0-v0.34.2, the consensus reactor is responsible for forming DuplicateVoteEvidence whenever double signs are observed. However, the current block is still “in flight” when it is being formed by the consensus reactor. It hasn’t been finalized through network consensus yet. This means that different nodes in the network may observe different “last commits” when assigning a timestamp to DuplicateVoteEvidence. In turn, different nodes could form DuplicateVoteEvidence objects at the same height but with different timestamps. One DuplicateVoteEvidence object (with one timestamp) will then eventually get finalized in the block, but this means that any DuplicateVoteEvidence with a different timestamp is considered invalid. Any node that formed invalid DuplicateVoteEvidence will continue to propose invalid evidence; its peers may see this, and choose to disconnect from this node. This bug means that double signs are DoS vectors in Tendermint Core v0.34.0-v0.34.2. Tendermint Core v0.34.3 is a security release which fixes this bug. As of v0.34.3, DuplicateVoteEvidence is no longer formed by the consensus reactor; rather, the consensus reactor passes the Votes themselves into the EvidencePool, which is now responsible for forming DuplicateVoteEvidence. The EvidencePool has timestamp info that should be consistent across the network, which means that DuplicateVoteEvidence formed in this reactor should have consistent timestamps. This release changes the API between the consensus and evidence reactors.
Severity: MEDIUM (CVSS v3 base score: 6.5)
Weakness: CWE-400 \u2014 Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
Repository: https://github.com/tendermint/tendermint
Files changed:
consensus/byzantine_test.go
consensus/state.go
evidence/pool.go
evidence/pool_test.go
node/node_test.go
state/services.go
test/maverick/consensus/state.go
Commit message: use correct source of evidence time

Conflicting votes are now sent to the evidence pool to form duplicate vote evidence only once
the height of the evidence is finished and the time of the block finalised.


Vulnerable code:
	// Adds consensus based evidence to the evidence pool. This function differs to
	// AddEvidence by bypassing verification and adding it immediately to the pool
	AddEvidenceFromConsensus(types.Evidence) error
			var timestamp time.Time
			if voteErr.VoteA.Height == cs.state.InitialHeight {
				timestamp = cs.state.LastBlockTime // genesis time
			} else {
				timestamp = sm.MedianTime(cs.LastCommit.MakeCommit(), cs.LastValidators)
			}
			// form duplicate vote evidence from the conflicting votes and send it across to the
			// evidence pool
			ev := types.NewDuplicateVoteEvidence(voteErr.VoteA, voteErr.VoteB, timestamp, cs.Validators)
			evidenceErr := cs.evpool.AddEvidenceFromConsensus(ev)
			if evidenceErr != nil {
				cs.Logger.Error("Failed to add evidence to the evidence pool", "err", evidenceErr)
			} else {
				cs.Logger.Debug("Added evidence to the evidence pool", "ev", ev)
			}
	// evidence from consensus if buffered to this slice, awaiting until the next height
	consensusBuffer []types.Evidence
		consensusBuffer: make([]types.Evidence, 0),
// Update pulls the latest state to be used for expiration and evidence params and then prunes all expired evidence
			"Failed EvidencePool.Update new state height is less than or equal to previous state height: %d <= %d",
	evpool.logger.Info("Updating evidence pool", "last_block_height", state.LastBlockHeight,
	evpool.logger.Info(
		"updating evidence pool",
		"last_block_height", state.LastBlockHeight,
		"last_block_time", state.LastBlockTime,
	)

	evpool.mtx.Lock()
	// flush awaiting evidence from consensus into pool
	evpool.flushConsensusBuffer()
	evpool.state = state
	evpool.mtx.Unlock()
		evpool.logger.Info("Evidence already pending, ignoring this one", "ev", ev)
// AddEvidenceFromConsensus should be exposed only to the consensus reactor so it can add evidence
// to the pool directly without the need for verification.
func (evpool *Pool) AddEvidenceFromConsensus(ev types.Evidence) error {

	// we already have this evidence, log this but don't return an error.
	if evpool.isPending(ev) {
		evpool.logger.Info("Evidence already pending, ignoring this one", "ev", ev)
		return nil
	}

	// add evidence to a buffer which will pass the evidence to the pool at the following height.
	// This avoids the issue of some nodes verifying and proposing evidence at a height where the
	// block hasn't been committed on cause others to potentially fail.
	evpool.consensusBuffer = append(evpool.consensusBuffer, ev)
	evpool.logger.Info("received new evidence of byzantine behavior from consensus", "evidence", ev)

	return nil
				return &types.ErrInvalidEvidence{Evidence: ev, Reason: err}
		evpool.logger.Info("Deleted pending evidence", "evidence", evidence)
// flushConsensusBuffer moves the evidence produced from consensus into the evidence pool
// and list so that it can be broadcasted and proposed
func (evpool *Pool) flushConsensusBuffer() {
	for _, ev := range evpool.consensusBuffer {
		if err := evpool.addPendingEvidence(ev); err != nil {
		evpool.evidenceList.PushBack(ev)
	evpool.consensusBuffer = make([]types.Evidence, 0)
func TestAddEvidenceFromConsensus(t *testing.T) {
	pool, val := defaultTestPool(height)
	ev := types.NewMockDuplicateVoteEvidenceWithValidator(height, defaultEvidenceTime, val, evidenceChainID)
	require.NoError(t, pool.AddEvidenceFromConsensus(ev))

	// shouldn't be able to submit the same evidence twice
	require.NoError(t, pool.AddEvidenceFromConsensus(ev))
	state = pool.State()
	state.LastBlockHeight++
	pool.Update(state, []types.Evidence{})
	evList2, _ := pool.PendingEvidence(defaultEvidenceMaxBytes)
	require.Equal(t, evList, evList2)
		err := evidencePool.AddEvidenceFromConsensus(ev)
		require.NoError(t, err)
func (EmptyEvidencePool) AddEvidence(types.Evidence) error              { return nil }
func (EmptyEvidencePool) Update(State, types.EvidenceList)              {}
func (EmptyEvidencePool) CheckEvidence(evList types.EvidenceList) error { return nil }
func (EmptyEvidencePool) AddEvidenceFromConsensus(evidence types.Evidence) error {
	return nil
}
	// Adds consensus based evidence to the evidence pool where time is the time
	// of the block where the offense occurred and the validator set is the current one.
	AddEvidenceFromConsensus(evidence types.Evidence) error
			var timestamp time.Time
			if voteErr.VoteA.Height == cs.state.InitialHeight {
				timestamp = cs.state.LastBlockTime // genesis time
			} else {
				timestamp = sm.MedianTime(cs.LastCommit.MakeCommit(), cs.LastValidators)
			}
			ev := types.NewDuplicateVoteEvidence(voteErr.VoteA, voteErr.VoteB, timestamp, cs.Validators)
			evidenceErr := cs.evpool.AddEvidenceFromConsensus(ev)
			if evidenceErr != nil {
				cs.Logger.Error("Failed to add evidence to the evidence pool", "err", evidenceErr)
			}

Fixed code:
	// introducing a lazy proposer means that the time of the block committed is different to the
	// timestamp that the other nodes have. This tests to ensure that the evidence that finally gets
	// proposed will have a valid timestamp
	lazyProposer := css[1]

	lazyProposer.decideProposal = func(height int64, round int32) {
		lazyProposer.Logger.Info("Lazy Proposer proposing condensed commit")
		if lazyProposer.privValidator == nil {
			panic("entered createProposalBlock with privValidator being nil")
		}

		var commit *types.Commit
		switch {
		case lazyProposer.Height == lazyProposer.state.InitialHeight:
			// We're creating a proposal for the first block.
			// The commit is empty, but not nil.
			commit = types.NewCommit(0, 0, types.BlockID{}, nil)
		case lazyProposer.LastCommit.HasTwoThirdsMajority():
			// Make the commit from LastCommit
			commit = lazyProposer.LastCommit.MakeCommit()
		default: // This shouldn't happen.
			lazyProposer.Logger.Error("enterPropose: Cannot propose anything: No commit for the previous block")
			return
		}

		// omit the last signature in the commit
		commit.Signatures[len(commit.Signatures)-1] = types.NewCommitSigAbsent()

		if lazyProposer.privValidatorPubKey == nil {
			// If this node is a validator & proposer in the current round, it will
			// miss the opportunity to create a block.
			lazyProposer.Logger.Error(fmt.Sprintf("enterPropose: %v", errPubKeyIsNotSet))
			return
		}
		proposerAddr := lazyProposer.privValidatorPubKey.Address()

		block, blockParts := lazyProposer.blockExec.CreateProposalBlock(
			lazyProposer.Height, lazyProposer.state, commit, proposerAddr,
		)

		// Flush the WAL. Otherwise, we may not recompute the same proposal to sign,
		// and the privValidator will refuse to sign anything.
		if err := lazyProposer.wal.FlushAndSync(); err != nil {
			lazyProposer.Logger.Error("Error flushing to disk")
		}

		// Make proposal
		propBlockID := types.BlockID{Hash: block.Hash(), PartSetHeader: blockParts.Header()}
		proposal := types.NewProposal(height, round, lazyProposer.ValidRound, propBlockID)
		p := proposal.ToProto()
		if err := lazyProposer.privValidator.SignProposal(lazyProposer.state.ChainID, p); err == nil {
			proposal.Signature = p.Signature

			// send proposal and block parts on internal msg queue
			lazyProposer.sendInternalMessage(msgInfo{&ProposalMessage{proposal}, ""})
			for i := 0; i < int(blockParts.Total()); i++ {
				part := blockParts.GetPart(i)
				lazyProposer.sendInternalMessage(msgInfo{&BlockPartMessage{lazyProposer.Height, lazyProposer.Round, part}, ""})
			}
			lazyProposer.Logger.Info("Signed proposal", "height", height, "round", round, "proposal", proposal)
			lazyProposer.Logger.Debug(fmt.Sprintf("Signed proposal block: %v", block))
		} else if !lazyProposer.replayMode {
			lazyProposer.Logger.Error("enterPropose: Error signing proposal", "height", height, "round", round, "err", err)
		}
	}

	// reports conflicting votes to the evidence pool to be processed into evidence
	ReportConflictingVotes(voteA, voteB *types.Vote)
			// report conflicting votes to the evidence pool
			cs.evpool.ReportConflictingVotes(voteErr.VoteA, voteErr.VoteB)
			cs.Logger.Info("Found and sent conflicting votes to the evidence pool",
				"VoteA", voteErr.VoteA,
				"VoteB", voteErr.VoteB,
			)
	// evidence from consensus is buffered to this slice, awaiting until the next height
	consensusBuffer []duplicateVoteSet
		consensusBuffer: make([]duplicateVoteSet, 0),
// Update takes both the new state and the evidence committed at that height and performs
// the following operations:
// 1. Take any conflicting votes from consensus and use the state's LastBlockTime to form
//    DuplicateVoteEvidence and add it to the pool.
// 2. Update the pool's state which contains evidence params relating to expiry.
// 3. Moves pending evidence that has now been committed into the committed pool.
// 4. Removes any expired evidence based on both height and time.
			"failed EvidencePool.Update new state height is less than or equal to previous state height: %d <= %d",
	evpool.logger.Debug("Updating evidence pool", "last_block_height", state.LastBlockHeight,
	// flush conflicting vote pairs from the buffer, producing DuplicateVoteEvidence and
	// adding it to the pool
	evpool.processConsensusBuffer(state)
	evpool.updateState(state)
		evpool.logger.Debug("Evidence already pending, ignoring this one", "ev", ev)
// ReportConflictingVotes takes two conflicting votes and forms duplicate vote evidence,
// adding it eventually to the evidence pool.
//
// Duplicate vote attacks happen before the block is committed and the timestamp is
// finalized, thus the evidence pool holds these votes in a buffer, forming the
// evidence from them once consensus at that height has been reached and `Update()` with
// the new state called.
//
// Votes are not verified.
func (evpool *Pool) ReportConflictingVotes(voteA, voteB *types.Vote) {
	evpool.consensusBuffer = append(evpool.consensusBuffer, duplicateVoteSet{
		VoteA: voteA,
		VoteB: voteB,
	})
				return err
		evpool.logger.Debug("Deleted pending evidence", "evidence", evidence)
func (evpool *Pool) updateState(state sm.State) {
	evpool.mtx.Lock()
	defer evpool.mtx.Unlock()
	evpool.state = state
}

// processConsensusBuffer converts all the duplicate votes witnessed from consensus
// into DuplicateVoteEvidence. It sets the evidence timestamp to the block height
// from the most recently committed block.
// Evidence is then added to the pool so as to be ready to be broadcasted and proposed.
func (evpool *Pool) processConsensusBuffer(state sm.State) {
	evpool.mtx.Lock()
	defer evpool.mtx.Unlock()
	for _, voteSet := range evpool.consensusBuffer {

		// Check the height of the conflicting votes and fetch the corresponding time and validator set
		// to produce the valid evidence
		var dve *types.DuplicateVoteEvidence
		switch {
		case voteSet.VoteA.Height == state.LastBlockHeight:
			dve = types.NewDuplicateVoteEvidence(
				voteSet.VoteA,
				voteSet.VoteB,
				state.LastBlockTime,
				state.LastValidators,
			)

		case voteSet.VoteA.Height < state.LastBlockHeight:
			valSet, err := evpool.stateDB.LoadValidators(voteSet.VoteA.Height)
			if err != nil {
				evpool.logger.Error("failed to load validator set for conflicting votes", "height",
					voteSet.VoteA.Height, "err", err,
				)
				continue
			}
			blockMeta := evpool.blockStore.LoadBlockMeta(voteSet.VoteA.Height)
			if blockMeta == nil {
				evpool.logger.Error("failed to load block time for conflicting votes", "height", voteSet.VoteA.Height)
				continue
			}
			dve = types.NewDuplicateVoteEvidence(
				voteSet.VoteA,
				voteSet.VoteB,
				blockMeta.Header.Time,
				valSet,
			)

		default:
			// evidence pool shouldn't expect to get votes from consensus of a height that is above the current
			// state. If this error is seen then perhaps consider keeping the votes in the buffer and retry
			// in following heights
			evpool.logger.Error("inbound duplicate votes from consensus are of a greater height than current state",
				"duplicate vote height", voteSet.VoteA.Height,
				"state.LastBlockHeight", state.LastBlockHeight)
			continue
		}

		// check if we already have this evidence
		if evpool.isPending(dve) {
			evpool.logger.Debug("evidence already pending; ignoring", "evidence", dve)
			continue
		}

		// check that the evidence is not already committed on chain
		if evpool.isCommitted(dve) {
			evpool.logger.Debug("evidence already committed; ignoring", "evidence", dve)
			continue
		}

		if err := evpool.addPendingEvidence(dve); err != nil {
		evpool.evidenceList.PushBack(dve)

		evpool.logger.Info("verified new evidence of byzantine behavior", "evidence", dve)
	evpool.consensusBuffer = make([]duplicateVoteSet, 0)
}

type duplicateVoteSet struct {
	VoteA *types.Vote
	VoteB *types.Vote
func TestReportConflictingVotes(t *testing.T) {
	pool, pv := defaultTestPool(height)
	val := types.NewValidator(pv.PrivKey.PubKey(), 10)
	ev := types.NewMockDuplicateVoteEvidenceWithValidator(height+1, defaultEvidenceTime, pv, evidenceChainID)

	pool.ReportConflictingVotes(ev.VoteA, ev.VoteB)

	// shouldn't be able to submit the same evidence twice
	pool.ReportConflictingVotes(ev.VoteA, ev.VoteB)
	state.LastBlockTime = ev.Time()
	state.LastValidators = types.NewValidatorSet([]*types.Validator{val})
		evidencePool.ReportConflictingVotes(ev.VoteA, ev.VoteB)
func (EmptyEvidencePool) AddEvidence(types.Evidence) error                { return nil }
func (EmptyEvidencePool) Update(State, types.EvidenceList)                {}
func (EmptyEvidencePool) CheckEvidence(evList types.EvidenceList) error   { return nil }
func (EmptyEvidencePool) ReportConflictingVotes(voteA, voteB *types.Vote) {}
	// reports conflicting votes to the evidence pool to be processed into evidence
	ReportConflictingVotes(voteA, voteB *types.Vote)
			cs.evpool.ReportConflictingVotes(voteErr.VoteA, voteErr.VoteB)