tree 0e5ae0a2eb4e0feaeb4b75bc449260f51ef90f82
parent 12e1027aa6c7687b5638c0c9260696266c9e400b
author Willy Tarreau <w@1wt.eu> 1616677949 +0100
committer Willy Tarreau <w@1wt.eu> 1616682606 +0100
encoding latin1

BUG/MINOR: http_fetch: make hdr_ip() reject trailing characters

The hdr_ip() sample fetch function will try to extract IP addresses
from a header field. These IP addresses are parsed using url2ipv4()
and if it fails it will fall back to inet_pton(AF_INET6), otherwise
will fail.

There is a small problem there which is that if a field starts with
an IP address and is immediately followed by some garbage, the IP
address part is still returned. This is a problem with fields such
as x-forwarded-for because it prevents detection of accidental
corruption or bug along the chain. For example, the following string:

   x-forwarded-for: 1.2.3.4; 5.6.7.8

or this one:

   x-forwarded-for: 1.2.3.4O    ( the last one being the letter 'O')

would still return "1.2.3.4" despite the trailing characters. This is
bad because it will silently cover broken code running on intermediary
proxies and may even in some cases allow haproxy to pass improperly
formatted headers after they were apparently validated, for example,
if someone extracts the address from this field to place it into
another one.

This issue would only affect the IPv4 parser, because the IPv6 parser
already uses inet_pton() which fails at the first invalid character and
rejects trailing port numbers.

In strict compliance with RFC7239, let's make sure that if there are any
characters left in the string, the parsing fails and makes hdr_ip()
return nothing. However, a special case has to be handled to support
IPv4 addresses followed by a colon and a valid port number, because till
now the parser used to implicitly accept them and it appears that this
practice, though rare, does exist at least in Azure:
   https://docs.microsoft.com/en-us/azure/application-gateway/how-application-gateway-works

This issue has always been there so the fix may be backported to all
versions. It will need the following commit in order to work as expected:

    MINOR: tools: make url2ipv4 return the exact number of bytes parsed

Many thanks to https://twitter.com/melardev and the BitMEX Security Team
for their detailed report.