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ftp: Introduce FTP::max_command_length

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oss-fuzz produced FTP traffic with a ~550KB long FTP command. Cap FTP command
length at 100 bytes, log a weird if a command is larger than that and move
on to the next. Likely it's not actual FTP traffic, but raising an
analyzer violation would allow clients an easy way to disable the analyzer
by sending an overly long command.

The added test PCAP was generated using a fake Python socket server/client.
This commit is contained in:
Arne Welzel 2022-11-15 21:27:53 +01:00
parent ee8e2decec
commit 3f5cb75a2a
10 changed files with 83 additions and 0 deletions
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1
scripts/base/frameworks/notice/weird.zeek
View file

@ -136,6 +136,7 @@ export {
["FIN_advanced_last_seq"] = ACTION_LOG,
["FIN_after_reset"] = ACTION_IGNORE,
["FIN_storm"] = ACTION_NOTICE_PER_ORIG,
["FTP_max_command_length_exceeded"] = ACTION_LOG_PER_CONN,
["FTP_too_many_pending_commands"] = ACTION_LOG_PER_CONN,
["HTTP_bad_chunk_size"] = ACTION_LOG,
["HTTP_chunked_transfer_for_multipart_message"] = ACTION_LOG,

9
scripts/base/init-bare.zeek
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@ -337,6 +337,15 @@ type ftp_port: record {
valid: bool; ##< True if format was right. Only then are *h* and *p* valid.
};
module FTP;
## Limits the size of commands accepted by the FTP analyzer. Longer commands
## raise a FTP_max_command_length_exceeded weird and are discarded.
const max_command_length = 100 &redef;
module GLOBAL;
## Statistics about what a TCP endpoint sent.
##
## .. zeek:see:: conn_stats

11
src/analyzer/protocol/ftp/FTP.cc
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@ -96,6 +96,17 @@ void FTP_Analyzer::DeliverStream(int length, const u_char* data, bool orig)
// Weird("FTP command missing", end_of_line - orig_line, orig_line);
cmd_str = new StringVal("<missing>");
}
else if ( BifConst::FTP::max_command_length > 0 &&
static_cast<zeek_uint_t>(cmd_len) > BifConst::FTP::max_command_length )
{
// If the FTP command is unusually long, log a weird if the analyzer
// has previously been confirmed, but otherwise just ignore the whole
// line and move on to the next.
if ( AnalyzerConfirmed() )
Weird("FTP_max_command_length_exceeded", util::fmt("%d", cmd_len));
return;
}
else
cmd_str = (new StringVal(cmd_len, cmd))->ToUpper();

2
src/const.bif
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@ -11,6 +11,8 @@ const exit_only_after_terminate: bool;
const digest_salt: string;
const max_analyzer_violations: count;
const FTP::max_command_length: count;
const NFS3::return_data: bool;
const NFS3::return_data_max: count;
const NFS3::return_data_first_only: bool;

11
testing/btest/Baseline/scripts.base.protocols.ftp.ftp-max-command-length/conn.log Normal file
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@ -0,0 +1,11 @@
### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
#separator \x09
#set_separator ,
#empty_field (empty)
#unset_field -
#path conn
#open XXXX-XX-XX-XX-XX-XX
#fields ts uid id.orig_h id.orig_p id.resp_h id.resp_p proto service duration orig_bytes resp_bytes conn_state local_orig local_resp missed_bytes history orig_pkts orig_ip_bytes resp_pkts resp_ip_bytes tunnel_parents
#types time string addr port addr port enum string interval count count string bool bool count string count count count count set[string]
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 tcp ftp 0.213412 358 313 SF - - 0 ShAdDaFf 23 1562 17 1205 -
#close XXXX-XX-XX-XX-XX-XX

11
testing/btest/Baseline/scripts.base.protocols.ftp.ftp-max-command-length/dpd.log Normal file
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@ -0,0 +1,11 @@
### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
#separator \x09
#set_separator ,
#empty_field (empty)
#unset_field -
#path dpd
#open XXXX-XX-XX-XX-XX-XX
#fields ts uid id.orig_h id.orig_p id.resp_h id.resp_p proto analyzer failure_reason
#types time string addr port addr port enum string string
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 tcp FTP FTP::max_command_length exceeded
#close XXXX-XX-XX-XX-XX-XX

15
testing/btest/Baseline/scripts.base.protocols.ftp.ftp-max-command-length/ftp.log Normal file
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@ -0,0 +1,15 @@
### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
#separator \x09
#set_separator ,
#empty_field (empty)
#unset_field -
#path ftp
#open XXXX-XX-XX-XX-XX-XX
#fields ts uid id.orig_h id.orig_p id.resp_h id.resp_p user password command arg mime_type file_size reply_code reply_msg data_channel.passive data_channel.orig_h data_channel.resp_h data_channel.resp_p fuid
#types time string addr port addr port string string string string string count count string bool addr addr port string
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 anonymous - USER anonymous - - 230 Response to USER command - - - - -
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 anonymous anonymous@zeek.org SYST - - - 200 Response to TYPEEEEEEEEEEEEE command - - - - -
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 anonymous anonymous@zeek.org PASV - - - 215 Response to SYSTTTTTTTTTTTTT command - - - - -
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 anonymous anonymous@zeek.org RETR ftp://127.0.0.1/./robots.txt - - 225 Response to RETR command - - - - -
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 anonymous anonymous@zeek.org PORT 114,115 - - 200 Response to PORT command - - - - -
#close XXXX-XX-XX-XX-XX-XX

11
testing/btest/Baseline/scripts.base.protocols.ftp.ftp-max-command-length/weird.log Normal file
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@ -0,0 +1,11 @@
### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
#separator \x09
#set_separator ,
#empty_field (empty)
#unset_field -
#path weird
#open XXXX-XX-XX-XX-XX-XX
#fields ts uid id.orig_h id.orig_p id.resp_h id.resp_p name addl notice peer source
#types time string addr port addr port string string bool string string
XXXXXXXXXX.XXXXXX CHhAvVGS1DHFjwGM9 127.0.0.1 58634 127.0.0.1 21 FTP_max_command_length_exceeded 132 F zeek FTP
#close XXXX-XX-XX-XX-XX-XX

BIN
testing/btest/Traces/ftp/fake-long-commands.pcap Normal file
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Binary file not shown.

12
testing/btest/scripts/base/protocols/ftp/ftp-max-command-length.zeek Normal file
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@ -0,0 +1,12 @@
# @TEST-DOC: Artificially generated pcap with FTP commands of length > 100. Verify generation of the involved logs.
#
# @TEST-EXEC: zeek -b -r $TRACES/ftp/fake-long-commands.pcap %INPUT
# @TEST-EXEC: btest-diff conn.log
# @TEST-EXEC: btest-diff ftp.log
# @TEST-EXEC: btest-diff weird.log
# @TEST-EXEC: test ! -f reporter.log
@load base/protocols/conn
@load base/protocols/ftp
redef FTP::logged_commands += { "USER", "SYST" };