ChainSafe · matthewkeil · Aug 7, 2026 · Aug 6, 2026 · Aug 7, 2026 · Aug 7, 2026
@@ -290,7 +290,12 @@ export function getBeaconBlockApi({
         if (blockLocallyProduced) {
           try {
             await verifyBlockProposerSignature(chain, signedBlock, blockRoot);
-            chain.seenBlockProposers.observeBlockRoot(slot, signedBlock.message.proposerIndex, blockRoot);
+            chain.seenBlockProposers.observeBlockRoot(
+              slot,
+              signedBlock.message.proposerIndex,
+              blockRoot,
+              signedBlockToSignedHeader(config, signedBlock)
+            );
           } catch (e) {
             chain.logger.error(
               "Proposer signature validation failed while publishing the block",

@@ -1,7 +1,12 @@
 import {ExecutionStatus, ProtoBlock} from "@lodestar/fork-choice";
 import {ForkName, ForkSeq, isForkPostFulu} from "@lodestar/params";
-import {DataAvailabilityStatus, IBeaconStateView, computeEpochAtSlot} from "@lodestar/state-transition";
-import {IndexedAttestation, Slot, deneb} from "@lodestar/types";
+import {
+  DataAvailabilityStatus,
+  IBeaconStateView,
+  computeEpochAtSlot,
+  signedBlockToSignedHeader,
+} from "@lodestar/state-transition";
+import {IndexedAttestation, Slot, deneb, ssz} from "@lodestar/types";
 import {toRootHex} from "@lodestar/utils";
 import {getBlobKzgCommitments} from "../../util/dataColumns.js";
 import type {BeaconChain} from "../chain.js";
@@ -207,10 +212,15 @@ export async function verifyBlocksInEpoch(
 
     if (opts.skipVerifyBlockSignatures !== true) {
       for (const block of blocks) {
-        const blockRoot = toRootHex(
-          this.config.getForkTypes(block.message.slot).BeaconBlock.hashTreeRoot(block.message)
-        );
-        this.seenBlockProposers.observeBlockRoot(block.message.slot, block.message.proposerIndex, blockRoot);
+        const {slot, proposerIndex} = block.message;
+        const signedBlockHeader = signedBlockToSignedHeader(this.config, block);
+        const blockRoot = toRootHex(ssz.phase0.BeaconBlockHeader.hashTreeRoot(signedBlockHeader.message));
+        this.seenBlockProposers.observeBlockRoot(slot, proposerIndex, blockRoot, signedBlockHeader);
+        // Only produce a slashing while importing the block. A block that is verified before it is published
+        // must not be treated as equivocation evidence since it may never be seen by the network
+        if (opts.verifyOnly !== true && this.seenBlockProposers.isEquivocating(slot, proposerIndex)) {
+          this.processProposerEquivocation(slot, proposerIndex);
+        }
       }
     }
 

@@ -130,6 +130,7 @@ import {CPStateDatastore} from "./stateCache/datastore/types.js";
 import {FIFOBlockStateCache} from "./stateCache/fifoBlockStateCache.js";
 import {PersistentCheckpointStateCache} from "./stateCache/persistentCheckpointsCache.js";
 import {CheckpointStateCache} from "./stateCache/types.js";
+import {validateApiProposerSlashing} from "./validation/proposerSlashing.js";
 import {ValidatorMonitor} from "./validatorMonitor.js";
 
 /**
@@ -200,6 +201,8 @@ export class BeaconChain implements IBeaconChain {
   readonly seenAggregatedAttestations: SeenAggregatedAttestations;
   readonly seenExecutionPayloadBids = new SeenExecutionPayloadBids();
   readonly seenBlockProposers = new SeenBlockProposers();
+  /** Proposer indexes with an in-flight proposer slashing production */
+  private readonly producingProposerSlashing = new Set<ValidatorIndex>();
   readonly seenSyncCommitteeMessages = new SeenSyncCommitteeMessages();
   readonly seenContributionAndProof: SeenContributionAndProof;
   readonly seenAttestationDatas: SeenAttestationDatas;
@@ -1163,6 +1166,59 @@ export class BeaconChain implements IBeaconChain {
     return this.payloadEnvelopeProcessor.processPayloadEnvelopeJob(payloadInput, opts);
   }
 
+  processProposerEquivocation(blockSlot: Slot, proposerIndex: ValidatorIndex): void {
+    this.produceProposerSlashing(blockSlot, proposerIndex).catch((e) => {
+      this.logger.debug("Error producing proposer slashing", {slot: blockSlot, proposerIndex}, e as Error);
+    });
+  }
+
+  /** Produce a proposer slashing from two conflicting signed block headers observed for the same slot and proposer */
+  private async produceProposerSlashing(blockSlot: Slot, proposerIndex: ValidatorIndex): Promise<void> {
+    if (
+      this.opts.disableProposerSlashings === true ||
+      this.opPool.hasSeenProposerSlashing(proposerIndex) ||
+      this.producingProposerSlashing.has(proposerIndex)
+    ) {
+      return;
+    }
+
+    const headers = this.seenBlockProposers.getEquivocationHeaders(blockSlot, proposerIndex);
+    if (headers === null) {
+      return;
+    }
+
+    this.producingProposerSlashing.add(proposerIndex);
+    try {
+      const [header1, header2] = headers;
+      // ProposerSlashing uses the bigint variant of the signed block header, see types package for details
+      const proposerSlashing: phase0.ProposerSlashing = {
+        signedHeader1: {
+          message: {...header1.message, slot: BigInt(header1.message.slot)},
+          signature: header1.signature,
+        },
+        signedHeader2: {
+          message: {...header2.message, slot: BigInt(header2.message.slot)},
+          signature: header2.signature,
+        },
+      };
+
+      try {
+        await validateApiProposerSlashing(this, proposerSlashing);
+      } catch (e) {
+        this.logger.debug("Produced proposer slashing is not valid", {slot: blockSlot, proposerIndex}, e as Error);
+        return;
+      }
+
+      this.opPool.insertProposerSlashing(proposerSlashing);
+      this.emitter.emit(routes.events.EventType.proposerSlashing, proposerSlashing);
+      this.emitter.emit(ChainEvent.publishProposerSlashing, proposerSlashing);
+      this.metrics?.opPool.proposerSlashingsProduced.inc();
+      this.logger.info("Produced proposer slashing from observed equivocation", {slot: blockSlot, proposerIndex});
+    } finally {
+      this.producingProposerSlashing.delete(proposerIndex);
+    }
+  }
+
   getStatus(): Status {
     const head = this.forkChoice.getHead();
     const finalizedCheckpoint = this.forkChoice.getFinalizedCheckpoint();

@@ -50,6 +50,11 @@ export enum ChainEvent {
    * and are ready to be published.
    */
   publishBlobSidecars = "publishBlobSidecars",
+  /**
+   * This event signals that a proposer slashing has been produced from an observed equivocation
+   * and is ready to be published.
+   */
+  publishProposerSlashing = "publishProposerSlashing",
   /**
    * Trigger an update of status so reqresp by peers have current earliestAvailableSlot
    */
@@ -110,6 +115,8 @@ export type IChainEvents = ApiEvents & {
 
   [ChainEvent.publishBlobSidecars]: (sidecars: deneb.BlobSidecar[]) => void;
 
+  [ChainEvent.publishProposerSlashing]: (proposerSlashing: phase0.ProposerSlashing) => void;
+
   [ChainEvent.updateStatus]: () => void;
 
   // Sync events that are chain->chain. Initiated from network requests but do not cross the network

@@ -262,6 +262,9 @@ export interface IBeaconChain {
   /** Process execution payload envelope: verify, import to fork choice, and persist to DB */
   processExecutionPayload(payloadInput: PayloadEnvelopeInput, opts?: ImportPayloadOpts): Promise<void>;
 
+  /** Produce and publish a proposer slashing from an observed equivocation. Does not throw, only logs errors */
+  processProposerEquivocation(blockSlot: Slot, proposerIndex: ValidatorIndex): void;
+
   getStatus(): Status;
 
   recomputeForkChoiceHead(caller: ForkchoiceCaller): ProtoBlock;

@@ -37,6 +37,8 @@ export type IChainOptions = BlockProcessOpts &
     suggestedFeeRecipient: string;
     graffitiAppend?: boolean;
     maxSkipSlots?: number;
+    /** Do not produce proposer slashings from observed equivocations and do not include proposer slashings in produced blocks */
+    disableProposerSlashings?: boolean;
     /** Ensure blobs returned by the execution engine are valid */
     sanityCheckExecutionEngineBlobs?: boolean;
     /** Max number of produced blobs by local validators to cache */
@@ -122,6 +124,7 @@ export const defaultChainOptions: IChainOptions = {
   // for gossip block validation, it's unlikely we see a reorg with 32 slots
   // for attestation validation, having this value ensures we don't have to regen states most of the time
   maxSkipSlots: 32,
+  disableProposerSlashings: false,
   broadcastValidationStrictness: "warn",
   // should be less than or equal to MIN_SIGNATURE_SETS_TO_BATCH_VERIFY
   // batching too much may block the I/O thread so if useWorker=false, suggest this value to be 32

@@ -1037,7 +1037,7 @@ export async function produceCommonBlockBody<T extends BlockType>(
     graffiti,
     // Eth1 data voting is no longer required since electra
     eth1Data: currentState.eth1Data,
-    proposerSlashings,
+    proposerSlashings: this.opts.disableProposerSlashings === true ? [] : proposerSlashings,
     attesterSlashings,
     attestations,
     // Since electra, deposits are processed by the execution layer,

@@ -1,5 +1,5 @@
 import {computeStartSlotAtEpoch} from "@lodestar/state-transition";
-import {Epoch, RootHex, Slot, ValidatorIndex} from "@lodestar/types";
+import {Epoch, RootHex, Slot, ValidatorIndex, phase0} from "@lodestar/types";
 import {MapDef} from "@lodestar/utils";
 
 /** Two distinct block roots signed by the same proposer for the same slot are sufficient to establish an equivocation */
@@ -13,41 +13,67 @@ const MAX_BLOCK_ROOTS_PER_PROPOSAL = 2;
  * equivocation evidence, but the block may still fail other validation. Such a block must not mark the proposal as
  * known, since that would cause a later valid block for the same slot and proposer to be ignored as a repeat proposal.
  *
+ * The signed block header of each observed root is kept so a proposer slashing can be produced from the two
+ * conflicting headers once an equivocation is established.
+ *
  * The cache is pruned on finalization and bounds the number of roots stored per proposer and slot
  */
 export class SeenBlockProposers {
   private readonly proposerIndexesBySlot = new MapDef<Slot, Set<ValidatorIndex>>(() => new Set<ValidatorIndex>());
-  private readonly blockRootsBySlot = new MapDef<Slot, MapDef<ValidatorIndex, Set<RootHex>>>(
-    () => new MapDef<ValidatorIndex, Set<RootHex>>(() => new Set<RootHex>())
-  );
+  private readonly signedBlockHeadersBySlot = new MapDef<
+    Slot,
+    MapDef<ValidatorIndex, Map<RootHex, phase0.SignedBeaconBlockHeader>>
+  >(() => new MapDef<ValidatorIndex, Map<RootHex, phase0.SignedBeaconBlockHeader>>(() => new Map()));
   private finalizedSlot: Slot = 0;
 
   isKnown(blockSlot: Slot, proposerIndex: ValidatorIndex): boolean {
     return this.proposerIndexesBySlot.get(blockSlot)?.has(proposerIndex) === true;
   }
 
   hasBlockRoot(blockSlot: Slot, proposerIndex: ValidatorIndex, blockRoot: RootHex): boolean {
-    return this.blockRootsBySlot.get(blockSlot)?.get(proposerIndex)?.has(blockRoot) === true;
+    return this.signedBlockHeadersBySlot.get(blockSlot)?.get(proposerIndex)?.has(blockRoot) === true;
   }
 
   isEquivocating(blockSlot: Slot, proposerIndex: ValidatorIndex): boolean {
-    return (this.blockRootsBySlot.get(blockSlot)?.get(proposerIndex)?.size ?? 0) >= MAX_BLOCK_ROOTS_PER_PROPOSAL;
+    return (
+      (this.signedBlockHeadersBySlot.get(blockSlot)?.get(proposerIndex)?.size ?? 0) >= MAX_BLOCK_ROOTS_PER_PROPOSAL
+    );
   }
 
   getConflictingBlockRoots(blockSlot: Slot, proposerIndex: ValidatorIndex, blockRoot: RootHex): RootHex[] {
-    const roots = this.blockRootsBySlot.get(blockSlot)?.get(proposerIndex);
-    return roots === undefined ? [] : Array.from(roots).filter((root) => root !== blockRoot);
+    const signedBlockHeaderByRoot = this.signedBlockHeadersBySlot.get(blockSlot)?.get(proposerIndex);
+    return signedBlockHeaderByRoot === undefined
+      ? []
+      : Array.from(signedBlockHeaderByRoot.keys()).filter((root) => root !== blockRoot);
+  }
+
+  /** Return the two signed block headers that establish an equivocation, or null if there is none */
+  getEquivocationHeaders(
+    blockSlot: Slot,
+    proposerIndex: ValidatorIndex
+  ): [phase0.SignedBeaconBlockHeader, phase0.SignedBeaconBlockHeader] | null {
+    const signedBlockHeaderByRoot = this.signedBlockHeadersBySlot.get(blockSlot)?.get(proposerIndex);
+    if (signedBlockHeaderByRoot === undefined || signedBlockHeaderByRoot.size < MAX_BLOCK_ROOTS_PER_PROPOSAL) {
+      return null;
+    }
+    const [signedHeader1, signedHeader2] = signedBlockHeaderByRoot.values();
+    return [signedHeader1, signedHeader2];
   }
 
   /** Record a block only after its proposer signature has been verified */
-  observeBlockRoot(blockSlot: Slot, proposerIndex: ValidatorIndex, blockRoot: RootHex): void {
+  observeBlockRoot(
+    blockSlot: Slot,
+    proposerIndex: ValidatorIndex,
+    blockRoot: RootHex,
+    signedBlockHeader: phase0.SignedBeaconBlockHeader
+  ): void {
     if (blockSlot < this.finalizedSlot) {
       throw Error(`blockSlot ${blockSlot} < finalizedSlot ${this.finalizedSlot}`);
     }
 
-    const blockRoots = this.blockRootsBySlot.getOrDefault(blockSlot).getOrDefault(proposerIndex);
-    if (blockRoots.size < MAX_BLOCK_ROOTS_PER_PROPOSAL) {
-      blockRoots.add(blockRoot);
+    const signedBlockHeaderByRoot = this.signedBlockHeadersBySlot.getOrDefault(blockSlot).getOrDefault(proposerIndex);
+    if (signedBlockHeaderByRoot.size < MAX_BLOCK_ROOTS_PER_PROPOSAL && !signedBlockHeaderByRoot.has(blockRoot)) {
+      signedBlockHeaderByRoot.set(blockRoot, signedBlockHeader);
     }
   }
 
@@ -67,9 +93,9 @@ export class SeenBlockProposers {
         this.proposerIndexesBySlot.delete(slot);
       }
     }
-    for (const slot of this.blockRootsBySlot.keys()) {
+    for (const slot of this.signedBlockHeadersBySlot.keys()) {
       if (slot < finalizedSlot) {
-        this.blockRootsBySlot.delete(slot);
+        this.signedBlockHeadersBySlot.delete(slot);
       }
     }
   }

@@ -23,8 +23,9 @@ import {
   getBlockProposerSignatureSet,
   isExecutionBlockBodyType,
   isStatePostBellatrix,
+  signedBlockToSignedHeader,
 } from "@lodestar/state-transition";
-import {RootHex, SignedBeaconBlock, deneb, gloas, isGloasBeaconBlock} from "@lodestar/types";
+import {RootHex, SignedBeaconBlock, deneb, gloas, isGloasBeaconBlock, ssz} from "@lodestar/types";
 import {byteArrayEquals, sleep, toRootHex} from "@lodestar/utils";
 import {BlockErrorCode, BlockGossipError, GossipAction} from "../errors/index.js";
 import {IBeaconChain} from "../interface.js";
@@ -75,7 +76,10 @@ export async function validateGossipBlock(
   // reboot if the `observed_block_producers` cache is empty. In that case, without this
   // check, we will load the parent and state from disk only to find out later that we
   // already know this block.
-  const blockRoot = toRootHex(config.getForkTypes(blockSlot).BeaconBlock.hashTreeRoot(block));
+  // A block's hash tree root is identical to its header's, so the root is derived from the header
+  // which is also used as potential equivocation evidence
+  const signedBlockHeader = signedBlockToSignedHeader(config, signedBlock);
+  const blockRoot = toRootHex(ssz.phase0.BeaconBlockHeader.hashTreeRoot(signedBlockHeader.message));
   if (chain.forkChoice.getBlockHexDefaultStatus(blockRoot) !== null) {
     throw new BlockGossipError(GossipAction.IGNORE, {code: BlockErrorCode.ALREADY_KNOWN, root: blockRoot});
   }
@@ -89,7 +93,7 @@ export async function validateGossipBlock(
   if (chain.seenBlockProposers.isKnown(blockSlot, proposerIndex)) {
     if (!hasBlockRoot && !chain.seenBlockProposers.isEquivocating(blockSlot, proposerIndex)) {
       await verifyBlockProposerSignature(chain, signedBlock, blockRoot, {verifyOnMainThread: false});
-      chain.seenBlockProposers.observeBlockRoot(blockSlot, proposerIndex, blockRoot);
+      chain.seenBlockProposers.observeBlockRoot(blockSlot, proposerIndex, blockRoot, signedBlockHeader);
     }
     throw new BlockGossipError(GossipAction.IGNORE, {code: BlockErrorCode.REPEAT_PROPOSAL, proposerIndex});
   }
@@ -276,7 +280,7 @@ export async function validateGossipBlock(
 
   // [REJECT] The proposer signature, signed_beacon_block.signature, is valid with respect to the proposer_index pubkey.
   await verifyBlockProposerSignature(chain, signedBlock, blockRoot);
-  chain.seenBlockProposers.observeBlockRoot(blockSlot, proposerIndex, blockRoot);
+  chain.seenBlockProposers.observeBlockRoot(blockSlot, proposerIndex, blockRoot, signedBlockHeader);
 
   // [REJECT] The block is proposed by the expected proposer_index for the block's slot in the context of the current
   // shuffling (defined by parent_root/slot). If the proposer_index cannot immediately be verified against the expected

@@ -1179,6 +1179,10 @@ export function createLodestarMetrics(
         name: "lodestar_oppool_proposer_slashing_pool_size",
         help: "Current size of the ProposerSlashingPool",
       }),
+      proposerSlashingsProduced: register.counter({
+        name: "lodestar_oppool_proposer_slashings_produced_total",
+        help: "Total number of proposer slashings produced from observed equivocations",
+      }),
       voluntaryExitPoolSize: register.gauge({
         name: "lodestar_oppool_voluntary_exit_pool_size",
         help: "Current size of the VoluntaryExitPool",

@@ -147,6 +147,7 @@ export class Network implements INetwork {
     this.chain.emitter.on(ChainEvent.updateTargetCustodyGroupCount, this.onTargetGroupCountUpdated);
     this.chain.emitter.on(ChainEvent.publishDataColumns, this.onPublishDataColumns);
     this.chain.emitter.on(ChainEvent.publishBlobSidecars, this.onPublishBlobSidecars);
+    this.chain.emitter.on(ChainEvent.publishProposerSlashing, this.onPublishProposerSlashing);
     this.chain.emitter.on(ChainEvent.updateStatus, this.onUpdateStatus);
   }
 
@@ -244,6 +245,7 @@ export class Network implements INetwork {
     this.chain.emitter.off(ChainEvent.updateTargetCustodyGroupCount, this.onTargetGroupCountUpdated);
     this.chain.emitter.off(ChainEvent.publishDataColumns, this.onPublishDataColumns);
     this.chain.emitter.off(ChainEvent.publishBlobSidecars, this.onPublishBlobSidecars);
+    this.chain.emitter.off(ChainEvent.publishProposerSlashing, this.onPublishProposerSlashing);
     this.chain.emitter.off(ChainEvent.updateStatus, this.onUpdateStatus);
     await this.core.close();
 
@@ -455,7 +457,8 @@ export class Network implements INetwork {
 
     return this.publishGossip<GossipType.proposer_slashing>(
       {type: GossipType.proposer_slashing, boundary},
-      proposerSlashing
+      proposerSlashing,
+      {ignoreDuplicatePublishError: true}
     );
   }
 
@@ -877,6 +880,18 @@ export class Network implements INetwork {
     return promiseAllMaybeAsync(sidecars.map((sidecar) => () => this.publishBlobSidecar(sidecar)));
   };
 
+  private onPublishProposerSlashing = async (proposerSlashing: phase0.ProposerSlashing): Promise<void> => {
+    try {
+      await this.publishProposerSlashing(proposerSlashing);
+    } catch (e) {
+      this.logger.debug(
+        "Error publishing proposer slashing",
+        {proposerIndex: proposerSlashing.signedHeader1.message.proposerIndex},
+        e as Error
+      );
+    }
+  };
+
   private onUpdateStatus = async (): Promise<void> => {
     await this.core.updateStatus(this.chain.getStatus());
   };

@@ -257,6 +257,13 @@ function getSequentialHandlers(modules: ValidatorFnsModules, options: GossipHand
         chain.seenPayloadEnvelopeInputCache.prune(blockRootHex);
       }
       throw e;
+    } finally {
+      // The block received from the network may have established an equivocation, either by conflicting
+      // with a previously observed block root (REPEAT_PROPOSAL) or with a root observed during validation
+      const proposerIndex = signedBlock.message.proposerIndex;
+      if (chain.seenBlockProposers.isEquivocating(slot, proposerIndex)) {
+        chain.processProposerEquivocation(slot, proposerIndex);
+      }
     }
   }
 

@@ -189,6 +189,7 @@ vi.mock("../../src/chain/chain.js", async (importActual) => {
       getStateBySlot: vi.fn(),
       updateBuilderStatus: vi.fn(),
       processBlock: vi.fn(),
+      processProposerEquivocation: vi.fn(),
       persistInvalidSszValue: vi.fn(),
       regenStateForAttestationVerification: vi.fn(),
       close: vi.fn(),