Backport of:

From 259b4f2e1fd01fbc55e569ee0a507afeae34f77c Mon Sep 17 00:00:00 2001
From: Patrick Monnerat <patrick@monnerat.net>
Date: Tue, 7 Sep 2021 13:26:42 +0200
Subject: [PATCH] ftp,imap,pop3,smtp: reject STARTTLS server response
 pipelining

If a server pipelines future responses within the STARTTLS response, the
former are preserved in the pingpong cache across TLS negotiation and
used as responses to the encrypted commands.

This fix detects pipelined STARTTLS responses and rejects them with an
error.

CVE-2021-22947

Bug: https://curl.se/docs/CVE-2021-22947.html
---
 lib/ftp.c               |  3 +++
 lib/imap.c              |  4 +++
 lib/pop3.c              |  4 +++
 lib/smtp.c              |  4 +++
 tests/data/Makefile.inc |  2 ++
 tests/data/test980      | 52 ++++++++++++++++++++++++++++++++++++
 tests/data/test981      | 59 +++++++++++++++++++++++++++++++++++++++++
 tests/data/test982      | 57 +++++++++++++++++++++++++++++++++++++++
 tests/data/test983      | 52 ++++++++++++++++++++++++++++++++++++
 9 files changed, 237 insertions(+)
 create mode 100644 tests/data/test980
 create mode 100644 tests/data/test981
 create mode 100644 tests/data/test982
 create mode 100644 tests/data/test983

--- a/lib/ftp.c
+++ b/lib/ftp.c
@@ -2703,6 +2703,9 @@ static CURLcode ftp_statemach_act(struct
     case FTP_AUTH:
       /* we have gotten the response to a previous AUTH command */
 
+      if(pp->cache_size)
+        return CURLE_WEIRD_SERVER_REPLY; /* Forbid pipelining in response. */
+
       /* RFC2228 (page 5) says:
        *
        * If the server is willing to accept the named security mechanism,
--- a/lib/imap.c
+++ b/lib/imap.c
@@ -948,6 +948,10 @@ static CURLcode imap_state_starttls_resp
 
   (void)instate; /* no use for this yet */
 
+  /* Pipelining in response is forbidden. */
+  if(data->conn->proto.imapc.pp.cache_size)
+    return CURLE_WEIRD_SERVER_REPLY;
+
   if(imapcode != IMAP_RESP_OK) {
     if(data->set.use_ssl != CURLUSESSL_TRY) {
       failf(data, "STARTTLS denied");
--- a/lib/pop3.c
+++ b/lib/pop3.c
@@ -755,6 +755,10 @@ static CURLcode pop3_state_starttls_resp
 
   (void)instate; /* no use for this yet */
 
+  /* Pipelining in response is forbidden. */
+  if(data->conn->proto.pop3c.pp.cache_size)
+    return CURLE_WEIRD_SERVER_REPLY;
+
   if(pop3code != '+') {
     if(data->set.use_ssl != CURLUSESSL_TRY) {
       failf(data, "STARTTLS denied");
--- a/lib/smtp.c
+++ b/lib/smtp.c
@@ -819,6 +819,10 @@ static CURLcode smtp_state_starttls_resp
 
   (void)instate; /* no use for this yet */
 
+  /* Pipelining in response is forbidden. */
+  if(data->conn->proto.smtpc.pp.cache_size)
+    return CURLE_WEIRD_SERVER_REPLY;
+
   if(smtpcode != 220) {
     if(data->set.use_ssl != CURLUSESSL_TRY) {
       failf(data, "STARTTLS denied, code %d", smtpcode);
--- a/tests/data/Makefile.inc
+++ b/tests/data/Makefile.inc
@@ -115,6 +115,8 @@ test945 test946 test947 test948 test949
 test954 test955 test956 test957 test958 test959 test960 test961 test962 \
 test963 test964 test965 test966 test967 test968 test969 test970 test971 \
 \
+test980 test981 test982 test983 \
+\
 test984 test985 test986 \
 \
 test1000 test1001 test1002 test1003 test1004 test1005 test1006 test1007 \
--- /dev/null
+++ b/tests/data/test980
@@ -0,0 +1,52 @@
+<testcase>
+<info>
+<keywords>
+SMTP
+STARTTLS
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<servercmd>
+CAPA STARTTLS
+AUTH PLAIN
+REPLY STARTTLS 454 currently unavailable\r\n235 Authenticated\r\n250 2.1.0 Sender ok\r\n250 2.1.5 Recipient ok\r\n354 Enter mail\r\n250 2.0.0 Accepted
+REPLY AUTH 535 5.7.8 Authentication credentials invalid
+</servercmd>
+</reply>
+
+#
+# Client-side
+<client>
+<features>
+SSL
+</features>
+<server>
+smtp
+</server>
+ <name>
+SMTP STARTTLS pipelined server response
+ </name>
+<stdin>
+mail body
+</stdin>
+ <command>
+smtp://%HOSTIP:%SMTPPORT/%TESTNUMBER --mail-rcpt recipient@example.com --mail-from sender@example.com -u user:secret --ssl --sasl-ir -T -
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+# 8 is CURLE_WEIRD_SERVER_REPLY
+<errorcode>
+8
+</errorcode>
+<protocol>
+EHLO %TESTNUMBER
+STARTTLS
+</protocol>
+</verify>
+</testcase>
--- /dev/null
+++ b/tests/data/test981
@@ -0,0 +1,59 @@
+<testcase>
+<info>
+<keywords>
+IMAP
+STARTTLS
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<servercmd>
+CAPA STARTTLS
+REPLY STARTTLS A002 BAD currently unavailable\r\nA003 OK Authenticated\r\nA004 OK Accepted
+REPLY LOGIN A003 BAD Authentication credentials invalid
+</servercmd>
+</reply>
+
+#
+# Client-side
+<client>
+<features>
+SSL
+</features>
+<server>
+imap
+</server>
+ <name>
+IMAP STARTTLS pipelined server response
+ </name>
+ <command>
+imap://%HOSTIP:%IMAPPORT/%TESTNUMBER -T log/upload%TESTNUMBER -u user:secret --ssl
+</command>
+<file name="log/upload%TESTNUMBER">
+Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
+From: Fred Foobar <foobar@example.COM>
+Subject: afternoon meeting
+To: joe@example.com
+Message-Id: <B27397-0100000@example.COM>
+MIME-Version: 1.0
+Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
+
+Hello Joe, do you think we can meet at 3:30 tomorrow?
+</file>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+# 8 is CURLE_WEIRD_SERVER_REPLY
+<errorcode>
+8
+</errorcode>
+<protocol>
+A001 CAPABILITY
+A002 STARTTLS
+</protocol>
+</verify>
+</testcase>
--- /dev/null
+++ b/tests/data/test982
@@ -0,0 +1,57 @@
+<testcase>
+<info>
+<keywords>
+POP3
+STARTTLS
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<servercmd>
+CAPA STLS USER
+REPLY STLS -ERR currently unavailable\r\n+OK user accepted\r\n+OK authenticated
+REPLY PASS -ERR Authentication credentials invalid
+</servercmd>
+<data nocheck="yes">
+From: me@somewhere
+To: fake@nowhere
+
+body
+
+--
+  yours sincerely
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<features>
+SSL
+</features>
+<server>
+pop3
+</server>
+ <name>
+POP3 STARTTLS pipelined server response
+ </name>
+ <command>
+pop3://%HOSTIP:%POP3PORT/%TESTNUMBER -u user:secret --ssl
+ </command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+# 8 is CURLE_WEIRD_SERVER_REPLY
+<errorcode>
+8
+</errorcode>
+<protocol>
+CAPA
+STLS
+</protocol>
+</verify>
+</testcase>
--- /dev/null
+++ b/tests/data/test983
@@ -0,0 +1,52 @@
+<testcase>
+<info>
+<keywords>
+FTP
+STARTTLS
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<servercmd>
+REPLY AUTH 500 unknown command\r\n500 unknown command\r\n331 give password\r\n230 Authenticated\r\n257 "/"\r\n200 OK\r\n200 OK\r\n200 OK\r\n226 Transfer complete
+REPLY PASS 530 Login incorrect
+</servercmd>
+</reply>
+
+# Client-side
+<client>
+<features>
+SSL
+</features>
+<server>
+ftp
+</server>
+ <name>
+FTP STARTTLS pipelined server response
+ </name>
+<file name="log/test%TESTNUMBER.txt">
+data
+    to
+      see
+that FTPS
+works
+  so does it?
+</file>
+ <command>
+--ssl --ftp-ssl-control ftp://%HOSTIP:%FTPPORT/%TESTNUMBER -T log/test%TESTNUMBER.txt -u user:secret -P %CLIENTIP
+</command>
+</client>
+
+# Verify data after the test has been "shot"
+<verify>
+# 8 is CURLE_WEIRD_SERVER_REPLY
+<errorcode>
+8
+</errorcode>
+<protocol>
+AUTH SSL
+</protocol>
+</verify>
+</testcase>
