High severity7.5NVD Advisory· Published Jun 9, 2026· Updated Jun 9, 2026

Puma PROXY Protocol v1 Accepts Repeated Protocol Headers on Persistent Connections

CVE-2026-47737

Description

Impact

Puma is vulnerable to source IP spoofing when set_remote_address proxy_protocol: :v1 is enabled and persistent connections are used.

PROXY protocol v1 is a connection-level protocol. Support was added to Puma in v5.5.0. A proxy sends one PROXY header at the beginning of a TCP connection, before any HTTP data. Puma incorrectly re-parsed PROXY protocol headers after each keep-alive request on the same connection. An attacker able to send HTTP requests through a trusted proxy could therefore inject a second PROXY header between HTTP requests. Puma would treat the injected header as authoritative for the next request and overwrite REMOTE_ADDR.

This can mislead applications or middleware that use REMOTE_ADDR for security decisions, rate limiting, auditing, or allow/deny lists.

Only deployments that explicitly enable PROXY protocol v1 are affected, and will have set:

set_remote_address proxy_protocol: :v1

Puma's default configuration is not affected. Deployments that do not use persistent connections to Puma are also not expected to be affected by this issue.

Patches

Users should upgrade to versions 7.2.1 or 8.0.2.

Workarounds

Disable PROXY protocol v1 parsing if it is not required:

   # remove/comment this:
   # set_remote_address proxy_protocol: :v1

Users can also disable persistent connections to Puma, for example:

enable_keep_alives false

References

Affected products

Puma/pumallm-fuzzy
Range: up to 7.2.1, up to 8.0.2

Patches

ebe9db3929ab

7.2.1 backport (#3947)

https://github.com/puma/pumaNate BerkopecMay 26, 2026Fixed in 7.2.1via ghsa-release-walk

commit

3 files changed · +100 −12

lib/puma/client.rb+27 −11 modified

@@ -157,7 +157,7 @@ def reset
       @parser.reset
       @io_buffer.reset
       @read_header = true
-      @read_proxy = !!@expect_proxy_proto
+      @read_proxy = !!@expect_proxy_proto && @requests_served.zero?
       @env = @proto_env.dup
       @parsed_bytes = 0
       @ready = false
@@ -211,20 +211,36 @@ def tempfile_close
     def try_to_parse_proxy_protocol
       if @read_proxy
         if @expect_proxy_proto == :v1
-          if @buffer.include? "\r\n"
-            if md = PROXY_PROTOCOL_V1_REGEX.match(@buffer)
-              if md[1]
-                @peerip = md[1].split(" ")[0]
+          crlf_index = @buffer.index "\r\n"
+
+          unless crlf_index
+            if "PROXY ".start_with? @buffer
+              return false
+            elsif @buffer.start_with? "PROXY "
+              if @buffer.bytesize >= PROXY_PROTOCOL_V1_MAX_LENGTH
+                raise ConnectionError, "PROXY protocol v1 line is too long"
               end
-              @buffer = md.post_match
+              return false
             end
-            # if the buffer has a \r\n but doesn't have a PROXY protocol
-            # request, this is just HTTP from a non-PROXY client; move on
+
             @read_proxy = false
-            return @buffer.size > 0
-          else
-            return false
+            return true
+          end
+
+          if @buffer.start_with?("PROXY ") && crlf_index + 2 > PROXY_PROTOCOL_V1_MAX_LENGTH
+            raise ConnectionError, "PROXY protocol v1 line is too long"
+          end
+
+          if md = PROXY_PROTOCOL_V1_REGEX.match(@buffer)
+            if md[1]
+              @peerip = md[1].split(" ")[0]
+            end
+            @buffer = md.post_match
           end
+          # if the buffer has a \r\n but doesn't have a PROXY protocol
+          # request, this is just HTTP from a non-PROXY client; move on
+          @read_proxy = false
+          return @buffer.size > 0
         end
       end
       true

lib/puma/const.rb+2 −1 modified

@@ -291,7 +291,8 @@ module Const
     # Banned keys of response header
     BANNED_HEADER_KEY = /\A(rack\.|status\z)/.freeze
 
-    PROXY_PROTOCOL_V1_REGEX = /^PROXY (?:TCP4|TCP6|UNKNOWN) ([^\r]+)\r\n/.freeze
+    PROXY_PROTOCOL_V1_REGEX = /\APROXY (?:TCP4|TCP6|UNKNOWN) ([^\r]+)\r\n/.freeze
+    PROXY_PROTOCOL_V1_MAX_LENGTH = 107
 
     # All constants are prefixed with `PIPE_` to avoid name collisions.
     module PipeRequest

test/test_puma_server.rb+71 −0 modified

@@ -1623,6 +1623,77 @@ def test_proxy_protocol
     assert_equal 'fd00::1', remote_addr
   end
 
+  def test_proxy_protocol_rejects_line_without_crlf_at_max_length
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do
+      [200, {}, ["Hello"]]
+    end
+
+    socket = new_socket
+    socket << "PROXY #{'A' * (Puma::Const::PROXY_PROTOCOL_V1_MAX_LENGTH - "PROXY ".bytesize)}"
+
+    assert_raises EOFError, Errno::ECONNABORTED, Errno::ECONNRESET do
+      socket.read_response(timeout: 1)
+    end
+  end
+
+  def test_proxy_protocol_allows_non_proxy_requests_over_max_length
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do
+      [200, {}, ["Hello"]]
+    end
+
+    response = send_http_read_response "GET /#{'a' * Puma::Const::PROXY_PROTOCOL_V1_MAX_LENGTH} HTTP/1.0\r\n\r\n"
+
+    assert_equal "HTTP/1.0 200 OK", response.status
+    assert_equal "Hello", response.body
+  end
+
+  def test_proxy_protocol_ignores_embedded_proxy_line_in_http_body
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do |env|
+      body = env['rack.input'].read
+      [200, {'Content-Length' => body.bytesize.to_s}, [body]]
+    end
+
+    body = "prefix\nPROXY TCP4 1.1.1.1 2.2.2.2 3 4\r\nsuffix"
+    response = send_http_read_response "POST / HTTP/1.1\r\nHost: test.com\r\nContent-Length: #{body.bytesize}\r\n\r\n#{body}"
+
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal body, response.body
+  end
+
+  def test_proxy_protocol_only_parses_first_request_on_connection
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do |env|
+      [200, {}, [env["REMOTE_ADDR"]]]
+    end
+
+    socket = send_proxy_v1_http("GET /one HTTP/1.1\r\nHost: test.com\r\n\r\n", "1.2.3.4")
+
+    response = socket.read_response
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal "1.2.3.4", response.body
+
+    socket << "PROXY TCP4 127.0.0.1 127.0.0.1 10000 80\r\nGET /two HTTP/1.1\r\nHost: test.com\r\nConnection: close\r\n\r\n"
+
+    assert_match %r{\AHTTP/1\.[01] 400 Bad Request\z}, socket.read_response.status
+  end
+
+  def test_proxy_protocol_allows_proxy_http_method_on_keep_alive
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1, supported_http_methods: :any) do |env|
+      [200, {}, [env["REMOTE_ADDR"]]]
+    end
+
+    socket = send_proxy_v1_http("GET /one HTTP/1.1\r\nHost: test.com\r\n\r\n", "1.2.3.4")
+
+    response = socket.read_response
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal "1.2.3.4", response.body
+
+    socket << "PROXY /two HTTP/1.1\r\nHost: test.com\r\nConnection: close\r\n\r\n"
+
+    response = socket.read_response
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal "1.2.3.4", response.body
+  end
+
   # To comply with the Rack spec, we have to split header field values
   # containing newlines into multiple headers.
   def assert_does_not_allow_http_injection(app, opts = {})

439c6136d9c2

8.0.2 backport (#3944)

https://github.com/puma/pumaNate BerkopecMay 26, 2026Fixed in 8.0.2via ghsa-release-walk

commit

3 files changed · +100 −12

lib/puma/client.rb+27 −11 modified

@@ -163,7 +163,7 @@ def reset
       @parser.reset
       @io_buffer.reset
       @read_header = true
-      @read_proxy = !!@expect_proxy_proto
+      @read_proxy = !!@expect_proxy_proto && @requests_served.zero?
       @env = @proto_env.dup
       @parsed_bytes = 0
       @ready = false
@@ -213,20 +213,36 @@ def tempfile_close
     def try_to_parse_proxy_protocol
       if @read_proxy
         if @expect_proxy_proto == :v1
-          if @buffer.include? "\r\n"
-            if md = PROXY_PROTOCOL_V1_REGEX.match(@buffer)
-              if md[1]
-                @peerip = md[1].split(" ")[0]
+          crlf_index = @buffer.index "\r\n"
+
+          unless crlf_index
+            if "PROXY ".start_with? @buffer
+              return false
+            elsif @buffer.start_with? "PROXY "
+              if @buffer.bytesize >= PROXY_PROTOCOL_V1_MAX_LENGTH
+                raise ConnectionError, "PROXY protocol v1 line is too long"
               end
-              @buffer = md.post_match
+              return false
             end
-            # if the buffer has a \r\n but doesn't have a PROXY protocol
-            # request, this is just HTTP from a non-PROXY client; move on
+
             @read_proxy = false
-            return @buffer.size > 0
-          else
-            return false
+            return true
+          end
+
+          if @buffer.start_with?("PROXY ") && crlf_index + 2 > PROXY_PROTOCOL_V1_MAX_LENGTH
+            raise ConnectionError, "PROXY protocol v1 line is too long"
+          end
+
+          if md = PROXY_PROTOCOL_V1_REGEX.match(@buffer)
+            if md[1]
+              @peerip = md[1].split(" ")[0]
+            end
+            @buffer = md.post_match
           end
+          # if the buffer has a \r\n but doesn't have a PROXY protocol
+          # request, this is just HTTP from a non-PROXY client; move on
+          @read_proxy = false
+          return @buffer.size > 0
         end
       end
       true

lib/puma/const.rb+2 −1 modified

@@ -291,7 +291,8 @@ module Const
     # Banned keys of response header
     BANNED_HEADER_KEY = /\A(rack\.|status\z)/.freeze
 
-    PROXY_PROTOCOL_V1_REGEX = /^PROXY (?:TCP4|TCP6|UNKNOWN) ([^\r]+)\r\n/.freeze
+    PROXY_PROTOCOL_V1_REGEX = /\APROXY (?:TCP4|TCP6|UNKNOWN) ([^\r]+)\r\n/.freeze
+    PROXY_PROTOCOL_V1_MAX_LENGTH = 107
 
     # All constants are prefixed with `PIPE_` to avoid name collisions.
     module PipeRequest

test/test_puma_server.rb+71 −0 modified

@@ -1528,6 +1528,77 @@ def test_proxy_protocol
     assert_equal 'fd00::1', remote_addr
   end
 
+  def test_proxy_protocol_rejects_line_without_crlf_at_max_length
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do
+      [200, {}, ["Hello"]]
+    end
+
+    socket = new_socket
+    socket << "PROXY #{'A' * (Puma::Const::PROXY_PROTOCOL_V1_MAX_LENGTH - "PROXY ".bytesize)}"
+
+    assert_raises EOFError, Errno::ECONNABORTED, Errno::ECONNRESET do
+      socket.read_response(timeout: 1)
+    end
+  end
+
+  def test_proxy_protocol_allows_non_proxy_requests_over_max_length
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do
+      [200, {}, ["Hello"]]
+    end
+
+    response = send_http_read_response "GET /#{'a' * Puma::Const::PROXY_PROTOCOL_V1_MAX_LENGTH} HTTP/1.0\r\n\r\n"
+
+    assert_equal "HTTP/1.0 200 OK", response.status
+    assert_equal "Hello", response.body
+  end
+
+  def test_proxy_protocol_ignores_embedded_proxy_line_in_http_body
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do |env|
+      body = env['rack.input'].read
+      [200, {'Content-Length' => body.bytesize.to_s}, [body]]
+    end
+
+    body = "prefix\nPROXY TCP4 1.1.1.1 2.2.2.2 3 4\r\nsuffix"
+    response = send_http_read_response "POST / HTTP/1.1\r\nHost: test.com\r\nContent-Length: #{body.bytesize}\r\n\r\n#{body}"
+
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal body, response.body
+  end
+
+  def test_proxy_protocol_only_parses_first_request_on_connection
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1) do |env|
+      [200, {}, [env["REMOTE_ADDR"]]]
+    end
+
+    socket = send_proxy_v1_http("GET /one HTTP/1.1\r\nHost: test.com\r\n\r\n", "1.2.3.4")
+
+    response = socket.read_response
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal "1.2.3.4", response.body
+
+    socket << "PROXY TCP4 127.0.0.1 127.0.0.1 10000 80\r\nGET /two HTTP/1.1\r\nHost: test.com\r\nConnection: close\r\n\r\n"
+
+    assert_match %r{\AHTTP/1\.[01] 400 Bad Request\z}, socket.read_response.status
+  end
+
+  def test_proxy_protocol_allows_proxy_http_method_on_keep_alive
+    server_run(remote_address: :proxy_protocol, remote_address_proxy_protocol: :v1, supported_http_methods: :any) do |env|
+      [200, {}, [env["REMOTE_ADDR"]]]
+    end
+
+    socket = send_proxy_v1_http("GET /one HTTP/1.1\r\nHost: test.com\r\n\r\n", "1.2.3.4")
+
+    response = socket.read_response
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal "1.2.3.4", response.body
+
+    socket << "PROXY /two HTTP/1.1\r\nHost: test.com\r\nConnection: close\r\n\r\n"
+
+    response = socket.read_response
+    assert_equal "HTTP/1.1 200 OK", response.status
+    assert_equal "1.2.3.4", response.body
+  end
+
   # To comply with the Rack spec, we have to split header field values
   # containing newlines into multiple headers.
   def assert_does_not_allow_http_injection(app, opts = {})

Vulnerability mechanics

No source-code context for this CVE — mechanics is only generated when we can read the actual fix diff. Without that, the four sections (root cause, attack vector, affected code, fix) would be speculation rather than analysis.

References

News mentions

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cvss	0.455
epss	0.000
exploit	0.000
kev	0.000
patch	-0.070
ransomware	0.000