diff --git a/app/controllers/concerns/signature_verification.rb b/app/controllers/concerns/signature_verification.rb
index 4dd0cac55..89dc828f4 100644
--- a/app/controllers/concerns/signature_verification.rb
+++ b/app/controllers/concerns/signature_verification.rb
@@ -93,11 +93,15 @@ module SignatureVerification
 
     return account unless verify_signature(account, signature, compare_signed_string).nil?
 
-    @signature_verification_failure_reason = "Verification failed for #{account.username}@#{account.domain} #{account.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)"
-    @signed_request_account = nil
+    fail_with! "Verification failed for #{account.username}@#{account.domain} #{account.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)"
   rescue SignatureVerificationError => e
-    @signature_verification_failure_reason = e.message
-    @signed_request_account = nil
+    fail_with! e.message
+  rescue HTTP::Error, OpenSSL::SSL::SSLError => e
+    fail_with! "Failed to fetch remote data: #{e.message}"
+  rescue Mastodon::UnexptectedResponseError
+    fail_with! 'Failed to fetch remote data (got unexpected reply from server)'
+  rescue Stoplight::Error::RedLight
+    fail_with! 'Fetching attempt skipped because of recent connection failure'
   end
 
   def request_body
@@ -106,6 +110,11 @@ module SignatureVerification
 
   private
 
+  def fail_with!(message)
+    @signature_verification_failure_reason = message
+    @signed_request_account = nil
+  end
+
   def signature_params
     @signature_params ||= begin
       raw_signature = request.headers['Signature']
@@ -138,7 +147,17 @@ module SignatureVerification
     digests = request.headers['Digest'].split(',').map { |digest| digest.split('=', 2) }.map { |key, value| [key.downcase, value] }
     sha256  = digests.assoc('sha-256')
     raise SignatureVerificationError, "Mastodon only supports SHA-256 in Digest header. Offered algorithms: #{digests.map(&:first).join(', ')}" if sha256.nil?
-    raise SignatureVerificationError, "Invalid Digest value. Computed SHA-256 digest: #{body_digest}; given: #{sha256[1]}" if body_digest != sha256[1]
+
+    return if body_digest == sha256[1]
+
+    digest_size = begin
+      Base64.strict_decode64(sha256[1].strip).length
+    rescue ArgumentError
+      raise SignatureVerificationError, "Invalid Digest value. The provided Digest value is not a valid base64 string. Given digest: #{sha256[1]}"
+    end
+
+    raise SignatureVerificationError, "Invalid Digest value. The provided Digest value is not a SHA-256 digest. Given digest: #{sha256[1]}" if digest_size != 32
+    raise SignatureVerificationError, "Invalid Digest value. Computed SHA-256 digest: #{body_digest}; given: #{sha256[1]}"
   end
 
   def verify_signature(account, signature, compare_signed_string)
@@ -216,19 +235,20 @@ module SignatureVerification
     end
 
     if key_id.start_with?('acct:')
-      stoplight_wrap_request { ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, '')) }
+      stoplight_wrap_request { ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, ''), suppress_errors: false) }
     elsif !ActivityPub::TagManager.instance.local_uri?(key_id)
       account   = ActivityPub::TagManager.instance.uri_to_resource(key_id, Account)
-      account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false) }
+      account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false, suppress_errors: false) }
       account
     end
-  rescue Mastodon::HostValidationError
-    nil
+  rescue Mastodon::PrivateNetworkAddressError => e
+    raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})"
+  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteAccountService::Error, ActivityPub::FetchRemoteKeyService::Error, Webfinger::Error => e
+    raise SignatureVerificationError, e.message
   end
 
   def stoplight_wrap_request(&block)
     Stoplight("source:#{request.remote_ip}", &block)
-      .with_fallback { nil }
       .with_threshold(1)
       .with_cool_off_time(5.minutes.seconds)
       .with_error_handler { |error, handle| error.is_a?(HTTP::Error) || error.is_a?(OpenSSL::SSL::SSLError) ? handle.call(error) : raise(error) }
@@ -237,6 +257,10 @@ module SignatureVerification
 
   def account_refresh_key(account)
     return if account.local? || !account.activitypub?
-    ActivityPub::FetchRemoteAccountService.new.call(account.uri, only_key: true)
+    ActivityPub::FetchRemoteAccountService.new.call(account.uri, only_key: true, suppress_errors: false)
+  rescue Mastodon::PrivateNetworkAddressError => e
+    raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})"
+  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteAccountService::Error, Webfinger::Error => e
+    raise SignatureVerificationError, e.message
   end
 end
diff --git a/app/lib/request.rb b/app/lib/request.rb
index f5123d776..eac04c798 100644
--- a/app/lib/request.rb
+++ b/app/lib/request.rb
@@ -208,7 +208,7 @@ class Request
 
         addresses.each do |address|
           begin
-            check_private_address(address)
+            check_private_address(address, host)
 
             sock     = ::Socket.new(address.is_a?(Resolv::IPv6) ? ::Socket::AF_INET6 : ::Socket::AF_INET, ::Socket::SOCK_STREAM, 0)
             sockaddr = ::Socket.pack_sockaddr_in(port, address.to_s)
@@ -264,10 +264,10 @@ class Request
 
       alias new open
 
-      def check_private_address(address)
+      def check_private_address(address, host)
         addr = IPAddr.new(address.to_s)
         return if private_address_exceptions.any? { |range| range.include?(addr) }
-        raise Mastodon::HostValidationError if PrivateAddressCheck.private_address?(addr)
+        raise Mastodon::PrivateNetworkAddressError, host if PrivateAddressCheck.private_address?(addr)
       end
 
       def private_address_exceptions
diff --git a/app/lib/webfinger.rb b/app/lib/webfinger.rb
index a681e0815..7c0c10c33 100644
--- a/app/lib/webfinger.rb
+++ b/app/lib/webfinger.rb
@@ -3,7 +3,7 @@
 class Webfinger
   class Error < StandardError; end
   class GoneError < Error; end
-  class RedirectError < StandardError; end
+  class RedirectError < Error; end
 
   class Response
     attr_reader :uri
diff --git a/app/services/activitypub/fetch_remote_account_service.rb b/app/services/activitypub/fetch_remote_account_service.rb
index 9d01f5386..d7d739c59 100644
--- a/app/services/activitypub/fetch_remote_account_service.rb
+++ b/app/services/activitypub/fetch_remote_account_service.rb
@@ -5,10 +5,12 @@ class ActivityPub::FetchRemoteAccountService < BaseService
   include DomainControlHelper
   include WebfingerHelper
 
+  class Error < StandardError; end
+
   SUPPORTED_TYPES = %w(Application Group Organization Person Service).freeze
 
   # Does a WebFinger roundtrip on each call, unless `only_key` is true
-  def call(uri, id: true, prefetched_body: nil, break_on_redirect: false, only_key: false)
+  def call(uri, id: true, prefetched_body: nil, break_on_redirect: false, only_key: false, suppress_errors: true)
     return if domain_not_allowed?(uri)
     return ActivityPub::TagManager.instance.uri_to_resource(uri, Account) if ActivityPub::TagManager.instance.local_uri?(uri)
 
@@ -18,38 +20,50 @@ class ActivityPub::FetchRemoteAccountService < BaseService
       else
         body_to_json(prefetched_body, compare_id: id ? uri : nil)
       end
+    rescue Oj::ParseError
+      raise Error, "Error parsing JSON-LD document #{uri}"
     end
 
-    return if !supported_context? || !expected_type? || (break_on_redirect && @json['movedTo'].present?)
+    raise Error, "Error fetching actor JSON at #{uri}" if @json.nil?
+    raise Error, "Unsupported JSON-LD context for document #{uri}" unless supported_context?
+    raise Error, "Unexpected object type for actor #{uri} (expected any of: #{SUPPORTED_TYPES})" unless expected_type?
+    raise Error, "Actor #{uri} has moved to #{@json['movedTo']}" if break_on_redirect && @json['movedTo'].present?
 
     @uri      = @json['id']
     @username = @json['preferredUsername']
     @domain   = Addressable::URI.parse(@uri).normalized_host
 
-    return unless only_key || verified_webfinger?
+    check_webfinger! unless only_key
 
     ActivityPub::ProcessAccountService.new.call(@username, @domain, @json, only_key: only_key, verified_webfinger: !only_key)
-  rescue Oj::ParseError
-    nil
+  rescue Error => e
+    Rails.logger.debug "Fetching account #{uri} failed: #{e.message}"
+    raise unless suppress_errors
   end
 
   private
 
-  def verified_webfinger?
+  def check_webfinger!
     webfinger                            = webfinger!("acct:#{@username}@#{@domain}")
     confirmed_username, confirmed_domain = split_acct(webfinger.subject)
 
-    return webfinger.link('self', 'href') == @uri if @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
+    if @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
+      raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
+      return
+    end
 
     webfinger                            = webfinger!("acct:#{confirmed_username}@#{confirmed_domain}")
     @username, @domain                   = split_acct(webfinger.subject)
 
-    return false unless @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
-    return false if webfinger.link('self', 'href') != @uri
+    unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
+      raise Webfinger::RedirectError, "Too many webfinger redirects for URI #{uri} (stopped at #{@username}@#{@domain})"
+    end
 
-    true
-  rescue Webfinger::Error
-    false
+    raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
+  rescue Webfinger::RedirectError => e
+    raise Error, e.message
+  rescue Webfinger::Error => e
+    raise Error, "Webfinger error when resolving #{@username}@#{@domain}: #{e.message}"
   end
 
   def split_acct(acct)
diff --git a/app/services/activitypub/fetch_remote_key_service.rb b/app/services/activitypub/fetch_remote_key_service.rb
index c48288b3b..01008d883 100644
--- a/app/services/activitypub/fetch_remote_key_service.rb
+++ b/app/services/activitypub/fetch_remote_key_service.rb
@@ -3,9 +3,11 @@
 class ActivityPub::FetchRemoteKeyService < BaseService
   include JsonLdHelper
 
+  class Error < StandardError; end
+
   # Returns account that owns the key
-  def call(uri, id: true, prefetched_body: nil)
-    return if uri.blank?
+  def call(uri, id: true, prefetched_body: nil, suppress_errors: true)
+    raise Error, 'No key URI given' if uri.blank?
 
     if prefetched_body.nil?
       if id
@@ -13,7 +15,7 @@ class ActivityPub::FetchRemoteKeyService < BaseService
         if person?
           @json = fetch_resource(@json['id'], true)
         elsif uri != @json['id']
-          return
+          raise Error, "Fetched URI #{uri} has wrong id #{@json['id']}"
         end
       else
         @json = fetch_resource(uri, id)
@@ -22,21 +24,29 @@ class ActivityPub::FetchRemoteKeyService < BaseService
       @json = body_to_json(prefetched_body, compare_id: id ? uri : nil)
     end
 
-    return unless supported_context?(@json) && expected_type?
-    return find_account(@json['id'], @json) if person?
+    raise Error, "Unable to fetch key JSON at #{uri}" if @json.nil?
+    raise Error, "Unsupported JSON-LD context for document #{uri}" unless supported_context?(@json)
+    raise Error, "Unexpected object type for key #{uri}" unless expected_type?
+    return find_account(@json['id'], @json, suppress_errors) if person?
 
     @owner = fetch_resource(owner_uri, true)
 
-    return unless supported_context?(@owner) && confirmed_owner?
+    raise Error, "Unable to fetch actor JSON #{owner_uri}" if @owner.nil?
+    raise Error, "Unsupported JSON-LD context for document #{owner_uri}" unless supported_context?(@owner)
+    raise Error, "Unexpected object type for actor #{owner_uri} (expected any of: #{SUPPORTED_TYPES})" unless expected_owner_type?
+    raise Error, "publicKey id for #{owner_uri} does not correspond to #{@json['id']}" unless confirmed_owner?
 
-    find_account(owner_uri, @owner)
+    find_account(owner_uri, @owner, suppress_errors)
+  rescue Error => e
+    Rails.logger.debug "Fetching key #{uri} failed: #{e.message}"
+    raise unless suppress_errors
   end
 
   private
 
-  def find_account(uri, prefetched_body)
+  def find_account(uri, prefetched_body, suppress_errors)
     account   = ActivityPub::TagManager.instance.uri_to_resource(uri, Account)
-    account ||= ActivityPub::FetchRemoteAccountService.new.call(uri, prefetched_body: prefetched_body)
+    account ||= ActivityPub::FetchRemoteAccountService.new.call(uri, prefetched_body: prefetched_body, suppress_errors: suppress_errors)
     account
   end
 
@@ -56,7 +66,11 @@ class ActivityPub::FetchRemoteKeyService < BaseService
     @owner_uri ||= value_or_id(@json['owner'])
   end
 
+  def expected_owner_type?
+    equals_or_includes_any?(@owner['type'], ActivityPub::FetchRemoteAccountService::SUPPORTED_TYPES)
+  end
+
   def confirmed_owner?
-    equals_or_includes_any?(@owner['type'], ActivityPub::FetchRemoteAccountService::SUPPORTED_TYPES) && value_or_id(@owner['publicKey']) == @json['id']
+    value_or_id(@owner['publicKey']) == @json['id']
   end
 end
diff --git a/app/services/activitypub/process_account_service.rb b/app/services/activitypub/process_account_service.rb
index 34750dba6..456b3524b 100644
--- a/app/services/activitypub/process_account_service.rb
+++ b/app/services/activitypub/process_account_service.rb
@@ -32,8 +32,6 @@ class ActivityPub::ProcessAccountService < BaseService
       process_duplicate_accounts! if @options[:verified_webfinger]
     end
 
-    return if @account.nil?
-
     after_protocol_change! if protocol_changed?
     after_key_change! if key_changed? && !@options[:signed_with_known_key]
     clear_tombstones! if key_changed?
diff --git a/app/services/resolve_account_service.rb b/app/services/resolve_account_service.rb
index b55e45409..e3b370968 100644
--- a/app/services/resolve_account_service.rb
+++ b/app/services/resolve_account_service.rb
@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 class ResolveAccountService < BaseService
-  include JsonLdHelper
   include DomainControlHelper
   include WebfingerHelper
   include Redisable
@@ -13,6 +12,7 @@ class ResolveAccountService < BaseService
   # @param [Hash] options
   # @option options [Boolean] :redirected Do not follow further Webfinger redirects
   # @option options [Boolean] :skip_webfinger Do not attempt any webfinger query or refreshing account data
+  # @option options [Boolean] :suppress_errors When failing, return nil instead of raising an error
   # @return [Account]
   def call(uri, options = {})
     return if uri.blank?
@@ -52,15 +52,15 @@ class ResolveAccountService < BaseService
     # either needs to be created, or updated from fresh data
 
     fetch_account!
-  rescue Webfinger::Error, Oj::ParseError => e
+  rescue Webfinger::Error => e
     Rails.logger.debug "Webfinger query for #{@uri} failed: #{e}"
-    nil
+    raise unless @options[:suppress_errors]
   end
 
   private
 
   def process_options!(uri, options)
-    @options = options
+    @options = { suppress_errors: true }.merge(options)
 
     if uri.is_a?(Account)
       @account  = uri
@@ -96,7 +96,7 @@ class ResolveAccountService < BaseService
     @username, @domain = split_acct(@webfinger.subject)
 
     unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
-      raise Webfinger::RedirectError, "The URI #{uri} tries to hijack #{@username}@#{@domain}"
+      raise Webfinger::RedirectError, "Too many webfinger redirects for URI #{uri} (stopped at #{@username}@#{@domain})"
     end
   rescue Webfinger::GoneError
     @gone = true
@@ -110,7 +110,7 @@ class ResolveAccountService < BaseService
     return unless activitypub_ready?
 
     with_lock("resolve:#{@username}@#{@domain}") do
-      @account = ActivityPub::FetchRemoteAccountService.new.call(actor_url)
+      @account = ActivityPub::FetchRemoteAccountService.new.call(actor_url, suppress_errors: @options[:suppress_errors])
     end
 
     @account
diff --git a/lib/exceptions.rb b/lib/exceptions.rb
index 0c677b660..3c5ba226b 100644
--- a/lib/exceptions.rb
+++ b/lib/exceptions.rb
@@ -25,4 +25,13 @@ module Mastodon
       end
     end
   end
+
+  class PrivateNetworkAddressError < HostValidationError
+    attr_reader :host
+
+    def initialize(host)
+      @host = host
+      super()
+    end
+  end
 end
diff --git a/spec/services/activitypub/fetch_remote_account_service_spec.rb b/spec/services/activitypub/fetch_remote_account_service_spec.rb
index aa13f0a9b..ec6f1f41d 100644
--- a/spec/services/activitypub/fetch_remote_account_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_account_service_spec.rb
@@ -119,6 +119,58 @@ RSpec.describe ActivityPub::FetchRemoteAccountService, type: :service do
       include_examples 'sets profile data'
     end
 
+    context 'when WebFinger returns a different URI' do
+      let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
+
+      before do
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+      end
+
+      it 'fetches resource' do
+        account
+        expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+      end
+
+      it 'looks up webfinger' do
+        account
+        expect(a_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com')).to have_been_made.once
+      end
+
+      it 'does not create account' do
+        expect(account).to be_nil
+      end
+    end
+
+    context 'when WebFinger returns a different URI after a redirection' do
+      let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
+
+      before do
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+        stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+      end
+
+      it 'fetches resource' do
+        account
+        expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+      end
+
+      it 'looks up webfinger' do
+        account
+        expect(a_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com')).to have_been_made.once
+      end
+
+      it 'looks up "redirected" webfinger' do
+        account
+        expect(a_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af')).to have_been_made.once
+      end
+
+      it 'does not create account' do
+        expect(account).to be_nil
+      end
+    end
+
     context 'with wrong id' do
       it 'does not create account' do
         expect(subject.call('https://fake.address/@foo', prefetched_body: Oj.dump(actor))).to be_nil
diff --git a/spec/services/resolve_account_service_spec.rb b/spec/services/resolve_account_service_spec.rb
index 8c302e1d8..654606bea 100644
--- a/spec/services/resolve_account_service_spec.rb
+++ b/spec/services/resolve_account_service_spec.rb
@@ -137,8 +137,8 @@ RSpec.describe ResolveAccountService, type: :service do
       stub_request(:get, 'https://evil.example.com/.well-known/webfinger?resource=acct:foo@evil.example.com').to_return(body: Oj.dump(webfinger2), headers: { 'Content-Type': 'application/jrd+json' })
     end
 
-    it 'returns new remote account' do
-      expect { subject.call('Foo@redirected.example.com') }.to raise_error Webfinger::RedirectError
+    it 'does not return a new remote account' do
+      expect(subject.call('Foo@redirected.example.com')).to be_nil
     end
   end