diff --git a/packages/cli/src/cmds/validator/keymanager/impl.ts b/packages/cli/src/cmds/validator/keymanager/impl.ts
index 8816f964a8ce..24bf653250eb 100644
--- a/packages/cli/src/cmds/validator/keymanager/impl.ts
+++ b/packages/cli/src/cmds/validator/keymanager/impl.ts
@@ -42,11 +42,13 @@ export class KeymanagerApi implements Api {
   }
 
   async listFeeRecipient({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["listFeeRecipient"]> {
+    this.assertValidKnownPubkey(pubkey);
     return {data: {pubkey, ethaddress: this.validator.validatorStore.getFeeRecipient(pubkey)}};
   }
 
   async setFeeRecipient({pubkey, ethaddress}: FeeRecipientData): ReturnType<Api["setFeeRecipient"]> {
     this.checkIfProposerWriteEnabled();
+    this.assertValidKnownPubkey(pubkey);
     this.validator.validatorStore.setFeeRecipient(pubkey, parseFeeRecipient(ethaddress));
     this.persistedKeysBackend.writeProposerConfig(pubkey, this.validator.validatorStore.getProposerConfig(pubkey));
     return {status: 202};
@@ -54,12 +56,14 @@ export class KeymanagerApi implements Api {
 
   async deleteFeeRecipient({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["deleteFeeRecipient"]> {
     this.checkIfProposerWriteEnabled();
+    this.assertValidKnownPubkey(pubkey);
     this.validator.validatorStore.deleteFeeRecipient(pubkey);
     this.persistedKeysBackend.writeProposerConfig(pubkey, this.validator.validatorStore.getProposerConfig(pubkey));
     return {status: 204};
   }
 
   async getGraffiti({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["getGraffiti"]> {
+    this.assertValidKnownPubkey(pubkey);
     const graffiti = this.validator.validatorStore.getGraffiti(pubkey);
     if (graffiti === undefined) {
       throw new ApiError(404, `No graffiti for pubkey ${pubkey}`);
@@ -69,6 +73,7 @@ export class KeymanagerApi implements Api {
 
   async setGraffiti({pubkey, graffiti}: GraffitiData): ReturnType<Api["setGraffiti"]> {
     this.checkIfProposerWriteEnabled();
+    this.assertValidKnownPubkey(pubkey);
     this.validator.validatorStore.setGraffiti(pubkey, graffiti);
     this.persistedKeysBackend.writeProposerConfig(pubkey, this.validator.validatorStore.getProposerConfig(pubkey));
     return {status: 202};
@@ -76,18 +81,21 @@ export class KeymanagerApi implements Api {
 
   async deleteGraffiti({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["deleteGraffiti"]> {
     this.checkIfProposerWriteEnabled();
+    this.assertValidKnownPubkey(pubkey);
     this.validator.validatorStore.deleteGraffiti(pubkey);
     this.persistedKeysBackend.writeProposerConfig(pubkey, this.validator.validatorStore.getProposerConfig(pubkey));
     return {status: 204};
   }
 
   async getGasLimit({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["getGasLimit"]> {
+    this.assertValidKnownPubkey(pubkey);
     const gasLimit = this.validator.validatorStore.getGasLimit(pubkey);
     return {data: {pubkey, gasLimit}};
   }
 
   async setGasLimit({pubkey, gasLimit}: GasLimitData): ReturnType<Api["setGasLimit"]> {
     this.checkIfProposerWriteEnabled();
+    this.assertValidKnownPubkey(pubkey);
     this.validator.validatorStore.setGasLimit(pubkey, gasLimit);
     this.persistedKeysBackend.writeProposerConfig(pubkey, this.validator.validatorStore.getProposerConfig(pubkey));
     return {status: 202};
@@ -95,6 +103,7 @@ export class KeymanagerApi implements Api {
 
   async deleteGasLimit({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["deleteGasLimit"]> {
     this.checkIfProposerWriteEnabled();
+    this.assertValidKnownPubkey(pubkey);
     this.validator.validatorStore.deleteGasLimit(pubkey);
     this.persistedKeysBackend.writeProposerConfig(pubkey, this.validator.validatorStore.getProposerConfig(pubkey));
     return {status: 204};
@@ -344,6 +353,7 @@ export class KeymanagerApi implements Api {
   }
 
   async getBuilderBoostFactor({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["getBuilderBoostFactor"]> {
+    this.assertValidKnownPubkey(pubkey);
     const builderBoostFactor = this.validator.validatorStore.getBuilderBoostFactor(pubkey);
     return {data: {pubkey, builderBoostFactor}};
   }
@@ -353,6 +363,7 @@ export class KeymanagerApi implements Api {
     builderBoostFactor,
   }: BuilderBoostFactorData): ReturnType<Api["setBuilderBoostFactor"]> {
     this.checkIfProposerWriteEnabled();
+    this.assertValidKnownPubkey(pubkey);
     this.validator.validatorStore.setBuilderBoostFactor(pubkey, builderBoostFactor);
     this.persistedKeysBackend.writeProposerConfig(pubkey, this.validator.validatorStore.getProposerConfig(pubkey));
     return {status: 202};
@@ -366,6 +377,8 @@ export class KeymanagerApi implements Api {
   }
 
   async getProposerConfig({pubkey}: {pubkey: PubkeyHex}): ReturnType<Api["getProposerConfig"]> {
+    this.assertValidKnownPubkey(pubkey);
+
     const config = this.validator.validatorStore.getProposerConfig(pubkey);
 
     const data: ProposerConfigResponse = {
@@ -383,10 +396,18 @@ export class KeymanagerApi implements Api {
   }
 
   async signVoluntaryExit({pubkey, epoch}: {pubkey: PubkeyHex; epoch?: Epoch}): ReturnType<Api["signVoluntaryExit"]> {
+    this.assertValidKnownPubkey(pubkey);
+    return {data: await this.validator.signVoluntaryExit(pubkey, epoch)};
+  }
+
+  private assertValidKnownPubkey(pubkey: PubkeyHex): void {
     if (!isValidatePubkeyHex(pubkey)) {
       throw new ApiError(400, `Invalid pubkey ${pubkey}`);
     }
-    return {data: await this.validator.signVoluntaryExit(pubkey, epoch)};
+
+    if (!this.validator.validatorStore.hasVotingPubkey(pubkey)) {
+      throw new ApiError(404, `Validator pubkey ${pubkey} not known`);
+    }
   }
 }
 
diff --git a/packages/validator/src/services/validatorStore.ts b/packages/validator/src/services/validatorStore.ts
index 0c66f576ffa0..e80c0b291ef5 100644
--- a/packages/validator/src/services/validatorStore.ts
+++ b/packages/validator/src/services/validatorStore.ts
@@ -251,7 +251,11 @@ export class ValidatorStore {
   }
 
   getGraffiti(pubkeyHex: PubkeyHex): string | undefined {
-    return this.validators.get(pubkeyHex)?.graffiti ?? this.defaultProposerConfig.graffiti;
+    const validatorData = this.validators.get(pubkeyHex);
+    if (validatorData === undefined) {
+      throw Error(`Validator pubkey ${pubkeyHex} not known`);
+    }
+    return validatorData.graffiti ?? this.defaultProposerConfig.graffiti;
   }
 
   setGraffiti(pubkeyHex: PubkeyHex, graffiti: string): void {