libcurl-security.3: don't try to filter IPv4 hosts based on the URL

Closes #6942
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Daniel Stenberg 2021-04-23 16:32:19 +02:00
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@ -5,7 +5,7 @@
.\" * | (__| |_| | _ <| |___
.\" * \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
@ -162,6 +162,12 @@ Allowing your application to connect to local hosts, be it the same machine
that runs the application or a machine on the same local network, might be
possible to exploit by an attacker who then perhaps can "port-scan" the
particular hosts - depending on how the application and servers acts.
.SH "IPv4 Addresses"
Some users might be tempted to filter access to local resources or similar
based on numerical IPv4 addresses used in URLs. This is a bad and error-prone
idea because of the many different ways a numerical IPv4 address can be
specified and libcurl accepts: one to four dot-separated fields using one of
or a mix of decimal, octal or hexadecimal encoding.
.SH "IPv6 Addresses"
libcurl will normally handle IPv6 addresses transparently and just as easily
as IPv4 addresses. That means that a sanitizing function that filters out