strict HTTP version validation

Note: This is unrelated to a reverse proxy potentially talking HTTP/3 to clients.
This is about the HTTP protocol version spoken to Gunicorn, which is HTTP/1.0 or HTTP/1.1.

Little legitimate need for processing HTTP 1 requests with ambiguous version numbers.
Broadly refuse.

Co-authored-by: Ben Kallus <benjamin.p.kallus.gr@dartmouth.edu>

gunicorn/config.py

@@ -2282,6 +2282,26 @@ class PermitUnconventionalHTTPMethod(Setting):
         """
 
 
+class PermitUnconventionalHTTPVersion(Setting):
+    name = "permit_unconventional_http_version"
+    section = "Server Mechanics"
+    cli = ["--permit-unconventional-http-version"]
+    validator = validate_bool
+    action = "store_true"
+    default = False
+    desc = """\
+        Permit HTTP version not matching conventions of 2023
+
+        This disables the refusal of likely malformed request lines.
+        It is unusual to specify HTTP 1 versions other than 1.0 and 1.1.
+
+        This option is provided to diagnose backwards-incompatible changes.
+        Use with care and only if necessary. May be removed in a future version.
+
+        .. versionadded:: 22.0.0
+        """
+
+
 class CasefoldHTTPMethod(Setting):
     name = "casefold_http_method"
     section = "Server Mechanics"

gunicorn/http/message.py

@@ -26,7 +26,8 @@ DEFAULT_MAX_HEADERFIELD_SIZE = 8190
 RFC9110_5_6_2_TOKEN_SPECIALS = r"!#$%&'*+-.^_`|~"
 TOKEN_RE = re.compile(r"[%s0-9a-zA-Z]+" % (re.escape(RFC9110_5_6_2_TOKEN_SPECIALS)))
 METHOD_BADCHAR_RE = re.compile("[a-z#]")
-VERSION_RE = re.compile(r"HTTP/(\d+)\.(\d+)")
+# usually 1.0 or 1.1 - RFC9112 permits restricting to single-digit versions
+VERSION_RE = re.compile(r"HTTP/(\d)\.(\d)")
 
 
 class Message(object):
@@ -438,6 +439,10 @@ class Request(Message):
         if match is None:
             raise InvalidHTTPVersion(bits[2])
         self.version = (int(match.group(1)), int(match.group(2)))
+        if not (1, 0) <= self.version < (2, 0):
+            # if ever relaxing this, carefully review Content-Encoding processing
+            if not self.cfg.permit_unconventional_http_version:
+                raise InvalidHTTPVersion(self.version)
 
     def set_body_reader(self):
         super().set_body_reader()

tests/requests/invalid/prefix_06.http

@@ -0,0 +1,4 @@
+GET /the/future HTTP/1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111.1\r\n
+Content-Length: 7\r\n
+\r\n
+Old Man

tests/requests/invalid/prefix_06.py

@@ -0,0 +1,5 @@
+from gunicorn.config import Config
+from gunicorn.http.errors import InvalidHTTPVersion
+
+cfg = Config()
+request = InvalidHTTPVersion

tests/requests/invalid/version_01.http

@@ -0,0 +1,2 @@
+GET /foo HTTP/0.99\r\n
+\r\n

tests/requests/invalid/version_01.py

@@ -0,0 +1,2 @@
+from gunicorn.http.errors import InvalidHTTPVersion
+request = InvalidHTTPVersion

tests/requests/invalid/version_02.http

@@ -0,0 +1,2 @@
+GET /foo HTTP/2.0\r\n
+\r\n

tests/requests/invalid/version_02.py

@@ -0,0 +1,2 @@
+from gunicorn.http.errors import InvalidHTTPVersion
+request = InvalidHTTPVersion