[PATCH] socks: return error if hostname too long for remote resolve

Prior to this change the state machine attempted to change the remote
resolve to a local resolve if the hostname was too long. Unfortunately
that did not always work as intended, leading to a security issue. And
when it did it's a privacy violation for users of socks5h that may
expect their DNS requests will not leak.

Bug: https://curl.se/docs/CVE-2023-38545.html

Backported by: Samuel Henrique <samueloph@debian.org>

Gbp-Pq: Name CVE-2023-38545.patch

diff --git a/lib/socks.c b/lib/socks.c
index c492d663c47384612a2877e9ce6fc288e7b7bdfa..bfd070281b47184a1936d0c4281ad867f66b0d73 100644 (file)
--- a/lib/socks.c
+++ b/lib/socks.c
@@ -585,11 +585,14 @@ static CURLproxycode do_SOCKS5(struct Curl_cfilter *cf,
       infof(data, "SOCKS5: connecting to HTTP proxy %s port %d",
             sx->hostname, sx->remote_port);
 
-    /* RFC1928 chapter 5 specifies max 255 chars for domain name in packet */
+    /* RFC1928 chapter 5 specifies max 255 chars for domain name in packet.
+       If remote resolve is enabled and the host is too long then error.
+       The user's resolve setting is not overridden because that could be a
+       privacy violation and unexpected. */
     if(!socks5_resolve_local && hostname_len > 255) {
-      infof(data, "SOCKS5: server resolving disabled for hostnames of "
-            "length > 255 [actual len=%zu]", hostname_len);
-      socks5_resolve_local = TRUE;
+      failf(data, "SOCKS5: the destination hostname is too long to be "
+            "resolved remotely by the proxy.");
+      return CURLPX_LONG_HOSTNAME;
     }
 
     if(auth & ~(CURLAUTH_BASIC | CURLAUTH_GSSAPI))
@@ -903,7 +906,7 @@ CONNECT_RESOLVE_REMOTE:
       }
       else {
         socksreq[len++] = 3;
-        socksreq[len++] = (char) hostname_len; /* one byte address length */
+        socksreq[len++] = (unsigned char) hostname_len; /* one byte length */
         memcpy(&socksreq[len], sx->hostname, hostname_len); /* w/o NULL */
         len += hostname_len;
       }

diff --git a/tests/data/Makefile.inc b/tests/data/Makefile.inc
index 2ec4936ec1aa75ed69d1d96ab716d1ca51608b7b..bdb5365fba94c2e0286eabdcb7256b1c96bbb7d1 100644 (file)
--- a/tests/data/Makefile.inc
+++ b/tests/data/Makefile.inc
@@ -101,7 +101,7 @@ test681 test682 test683 test684 test685 test686 test687 test688 \
 \
 test700 test701 test702 test703 test704 test705 test706 test707 test708 \
 test709 test710 test711 test712 test713 test714 test715 test716 test717 \
-test718 test719 test720 test721 \
+test718 test719 test720 test721 test728\
 \
 test799 test800 test801 test802 test803 test804 test805 test806 test807 \
 test808 test809 test810 test811 test812 test813 test814 test815 test816 \

diff --git a/tests/data/test728 b/tests/data/test728
new file mode 100644 (file)
index 0000000..05bcf28
--- /dev/null
+++ b/tests/data/test728
@@ -0,0 +1,64 @@
+<testcase>
+<info>
+<keywords>
+HTTP
+HTTP GET
+SOCKS5
+SOCKS5h
+followlocation
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+# The hostname in this redirect is 256 characters and too long (> 255) for
+# SOCKS5 remote resolve. curl must return error CURLE_PROXY in this case.
+<data>
+HTTP/1.1 301 Moved Permanently
+Location: http://AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/
+Content-Length: 0
+Connection: close
+
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<features>
+proxy
+</features>
+<server>
+http
+socks5
+</server>
+ <name>
+SOCKS5h with HTTP redirect to hostname too long
+ </name>
+ <command>
+--no-progress-meter --location --proxy socks5h://%HOSTIP:%SOCKSPORT http://%HOSTIP:%HTTPPORT/%TESTNUMBER
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<protocol crlf="yes">
+GET /%TESTNUMBER HTTP/1.1
+Host: %HOSTIP:%HTTPPORT
+User-Agent: curl/%VERSION
+Accept: */*
+
+</protocol>
+<errorcode>
+97
+</errorcode>
+# the error message is verified because error code CURLE_PROXY (97) may be
+# returned for any number of reasons and we need to make sure it is
+# specifically for the reason below so that we know the check is working.
+<stderr mode="text">
+curl: (97) SOCKS5: the destination hostname is too long to be resolved remotely by the proxy.
+</stderr>
+</verify>
+</testcase>