fix: prevent SSRF via absolute URL bypassing base_uri

lib/httparty/exceptions.rb

@@ -59,4 +59,8 @@ class DuplicateLocationHeader < ResponseError; end
 
   # Exception that is raised when common network errors occur.
   class NetworkError < Foul; end
+
+  # Exception that is raised when an absolute URI is used that doesn't match
+  # the configured base_uri, which could indicate an SSRF attempt.
+  class UnsafeURIError < Foul; end
 end

lib/httparty/request.rb

@@ -113,6 +113,8 @@ def uri
         new_uri = path.clone
       end
 
+      validate_uri_safety!(new_uri) unless redirect
+
       # avoid double query string on redirects [#12]
       unless redirect
         new_uri.query = query_string(new_uri)
@@ -442,5 +444,23 @@ def encode_text(text, content_type)
         assume_utf16_is_big_endian: assume_utf16_is_big_endian
       ).call
     end
+
+    def validate_uri_safety!(new_uri)
+      return if options[:skip_uri_validation]
+
+      configured_base_uri = options[:base_uri]
+      return unless configured_base_uri
+
+      normalized_base = options[:uri_adapter].parse(
+        HTTParty.normalize_base_uri(configured_base_uri)
+      )
+
+      return if new_uri.host == normalized_base.host
+
+      raise UnsafeURIError,
+        "Requested URI '#{new_uri}' has host '#{new_uri.host}' but the " \
+        "configured base_uri '#{normalized_base}' has host '#{normalized_base.host}'. " \
+        "This request could send credentials to an unintended server."
+    end
   end
 end

spec/httparty/request_spec.rb

@@ -384,6 +384,74 @@
         end
       end
     end
+
+    context "URI safety validation" do
+      context "when base_uri is configured" do
+        it "raises UnsafeURIError when path is an absolute URL with different host" do
+          request = HTTParty::Request.new(
+            Net::HTTP::Get,
+            'http://evil.com/steal-data',
+            base_uri: 'http://trusted.com'
+          )
+          expect { request.uri }.to raise_error(
+            HTTParty::UnsafeURIError,
+            /has host 'evil.com' but the configured base_uri .* has host 'trusted.com'/
+          )
+        end
+
+        it "allows requests when path host matches base_uri host" do
+          request = HTTParty::Request.new(
+            Net::HTTP::Get,
+            'http://trusted.com/api/data',
+            base_uri: 'http://trusted.com'
+          )
+          expect { request.uri }.not_to raise_error
+          expect(request.uri.host).to eq('trusted.com')
+        end
+
+        it "allows relative paths" do
+          request = HTTParty::Request.new(
+            Net::HTTP::Get,
+            '/api/data',
+            base_uri: 'http://trusted.com'
+          )
+          expect { request.uri }.not_to raise_error
+          expect(request.uri.to_s).to eq('http://trusted.com/api/data')
+        end
+
+        it "raises UnsafeURIError for network-relative URLs with different host" do
+          @request.last_uri = URI.parse("https://trusted.com")
+          @request.path = URI.parse("//evil.com/steal")
+          @request.redirect = true
+          @request.options[:base_uri] = 'http://trusted.com'
+
+          # During redirects, URI safety is not checked to allow legitimate redirects
+          expect { @request.uri }.not_to raise_error
+        end
+
+        it "can be bypassed with skip_uri_validation option" do
+          request = HTTParty::Request.new(
+            Net::HTTP::Get,
+            'http://other.com/api/data',
+            base_uri: 'http://trusted.com',
+            skip_uri_validation: true
+          )
+          expect { request.uri }.not_to raise_error
+          expect(request.uri.host).to eq('other.com')
+        end
+      end
+
+      context "when base_uri is not configured" do
+        it "allows absolute URLs" do
+          request = HTTParty::Request.new(
+            Net::HTTP::Get,
+            'http://any-server.com/api/data'
+          )
+          expect { request.uri }.not_to raise_error
+          expect(request.uri.host).to eq('any-server.com')
+        end
+      end
+    end
   end
 
   describe "#setup_raw_request" do

spec/support/stub_response.rb

@@ -29,7 +29,9 @@ def response.read_body(&block)
 
     def stub_response(body, code = '200')
       code = code.to_s
-      @request.options[:base_uri] ||= 'http://localhost'
+      # Only set default base_uri if path is relative (has no host)
+      # This avoids triggering URI safety validation for absolute URLs in tests
+      @request.options[:base_uri] ||= 'http://localhost' if @request.path.relative?
       unless defined?(@http) && @http
         @http = Net::HTTP.new('localhost', 80)
         allow(@request).to receive(:http).and_return(@http)