Varnish forwards HTTP/1.1 requests with invalid methods #4318
Description
Expected Behavior
The HTTP RFCs specify that request methods must consist only of the following characters:
"!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA
Current Behavior
Varnish doesn't enforce this rule. Instead, it accepts and forwards methods containing the following disallowed bytes:
"(),/:;<=>?@[\\]{}- The full range from
\x80to\xff.
Possible Solution
Reject all requests containing disallowed bytes in methods.
Steps to Reproduce (for bugs)
- Start Varnish
- Send it a request with a super invalid method:
printf '"(),/:;<=>?@[\\]{}\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff / HTTP/1.1\r\nHost: a\r\n\r\n'' | ncat localhost 80- Observe that it gets forwarded as-is.
Context
I am differential testing HTTP implementations to find request smuggling vulnerabilities. While I have not demonstrated that this bug is exploitable, I figured that you might be interested.
Varnish Cache version
varnishd (varnish-trunk revision f778ad5) Copyright (c) 2006 Verdens Gang AS Copyright (c) 2006-2025 Varnish Software Copyright 2010-2025 UPLEX - Nils Goroll Systemoptimierung
Operating system
Debian 13
Source of binary packages used (if any)
No response