Обнаружение вредоносного кода в зашифрованном с помощью TLS трафике (без дешифровки)
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Обнаружение вредоносного кода в зашифрованном с помощью TLS трафике (без дешифровки)
- 1. Deciphering Malware’s Use of TLS (without Decryption) Ruslan Ivanov Consulting Systems Engineer, Cisco ruivanov@cisco.com
- 2. В докладе рассматривается работа группы исследователей компании Cisco, доказывающая применимость традиционных методов статистического и поведенческого анализа для обнаружения и атрибуции вредоносного ПО, использующего TLS в качестве метода шифрования каналов взаимодействия, без дешифровки или компрометации TLS-сессии. О чём этот доклад?
- 3. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public People Blake Anderson – Technical Leader PhD in Computer Science (Machine Learning) Started at Cisco in 2015 David McGrew – Cisco Fellow PhD in Physics (Chaos Theory) Started at Cisco in 1998 BRKSEC-2809 3
- 4. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Problem: Encrypted Malware Traffic • TLS usage increasing (this is not bad!) • String-matching solutions less ineffective • MITM problems • Privacy, legal, deployment, expense, non-cooperating clients InternetPremises BRKSEC-2809 4
- 5. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Our Approach: Leverage All Data Features InternetPremises Netflow data: SrcIP, DstIP, SrcPort, DstPort, Proto, #Bytes, #Packets Intraflow data: Packet Lengths & Inter-arrival Times, Byte Distribution, … TLS metadata: Extensions, Ciphersuites, SNI, Certificate Strings, … DNS data: Names and TTLs of linked responses HTTP data: Headers and File Magic for other flows from target 5BRKSEC-2809
- 6. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Flow Monitoring Export Collection Analysis StorageObservation Observation Observation srcIP, dstIP, srcPort, dstPort, prot, startTime, stopTime, numBytes, numPackets BRKSEC-2809 6
- 7. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Enhanced Telemetry Export Collection Analysis StorageObservation Observation Observation srcIP, dstIP, srcPort, dstPort, prot, startTime, stopTime, numBytes, numPackets New Data Features BRKSEC-2809 7
- 8. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Solution Overview OS inference Endpoint Context OS, Applications, PMTU, RTT, Infection, … ETTA data flow record labels flow record fingerprint rules classifier description Cisco Products ETTA data Application inference Malware Detection Malware Family Crypto Audit BRKSEC-2809 8
- 9. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Data Collection Training/Storage • Metadata • Packet lengths • TLS • DNS • HTTP Benign Records Malware Records Classifier/Rules BRKSEC-2809 9BRKSEC-2809 9
- 10. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Malware Benign • ThreatGRID pcaps • 5-minute sandbox runs • Threat Score = 100/100 • Millions of pcap’s • ~5,000-15,000 new pcap’s a day • Hundreds of millions of flows • Enterprise DMZ • ~10-15 million flows per day • ~500 user site • IP addresses are anonymized BRKSEC-2809 10
- 11. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Exploring Threat Data Features at Scale joy pcap2flowpcap json pcap2flow json Offline Online exporter jsoncollector https://github.com/cisco/joy Bill Hudson Philip Perricone 11BRKSEC-2809
- 12. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public src dst • SPLT – Sequence of Packet Lengths and Arrival Times • Byte Distribution • Byte Entropy Enhanced Telemetry Data Types 12BRKSEC-2809
- 13. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Sequence of Packet Lengths and Times src dst ClientpacketsServerpackets Time BRKSEC-2809 13
- 14. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Byte Distribution 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b H T T P / 1 . 1 2 0 0 O K BRKSEC-2809 14
- 15. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Byte Distribution 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b H T T P / 1 . 1 2 0 0 O K 1 BRKSEC-2809 15
- 16. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Byte Distribution 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b H T T P / 1 . 1 2 0 0 O K 1 1 BRKSEC-2809 16
- 17. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Byte Distribution 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b H T T P / 1 . 1 2 0 0 O K 1 2 BRKSEC-2809 17
- 18. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Byte Distribution 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b H T T P / 1 . 1 2 0 0 O K 1 1 2 BRKSEC-2809 18
- 19. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public TLS Handshake Protocol Client Server ClientHello ServerHello / Certificate ClientKeyExchange / ChangeCipherSpec Application Data ChangeCipherSpec BRKSEC-2809 19
- 20. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • Most popular TLS clients: • IE 8/11*, Tor, Opera • Wide variety in the number of distinct ciphersuite offer vectors • Some malware families only used one while others used hundreds • 2048-bit DHE_RSA was by far the most popular public key algorithm / size TLS Clients BRKSEC-2809 20
- 21. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • Most popular servers (taken from the certificate subject): • Bitcoin wallet (e.g., block.io) • File sharing sites (e.g., dropbox.com) • Advertising (e.g., criteo.com) • Search engines (e.g., google.com, baidu.com) • DGA-like certificate subjects were very common • .7% (as opposed to .09% on an enterprise network) used self-signed certificates • TLS_RSA_WITH_3DES_EDE_CBC_SHA was the most popular selected ciphersuite • These features are heavily dependent on the malware family TLS Servers BRKSEC-2809 21
- 22. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • Retain original capitalization • User-Agent vs user-agent vs User-agent vs USER-AGENT vs User-AgEnt • Retain original ordering of header fields • Absence or presence of HTTP fields gives information about environment • via, x-imforwards • Common User-Agent values: • Opera/9.50(WindowsNT6.0;U;en) • Mozilla/5.0(Windows;U;WindowsNT5.1;en- US;rv:1.9.2.3)Gecko/20100401Firefox/3.6.1(.NETCLR3.5.30731) • Mozilla/5.0(WindowsNT6.3;WOW64;Trident/7.0;Touch;rv:11.0)likeGecko HTTP Fields BRKSEC-2809 22
- 23. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • Common TTL values: • 100 > 300 > 60 > 3600 • Number of IPs per request: • 1 > 4 > 11 > 2 > 6 • Most common suffixes: • com > net > pl > eu > org • ~95% not found in the Alexa top-1,000,000 list DNS Information BRKSEC-2809 23
- 24. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Server Name Indication • Extension type: server_name (0x0000) • Indication from the client about the hostname of the server Record Headers ClientHello Random Nonce [Session ID] Cipher suites Compression Methods Extensions Single Extension BRKSEC-2809 24
- 25. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Certificate Information • Check for self-signed certificates • Issuer == Subject • Check for certificates not within validity period • Check for discrepancies in the SubjectAltName (optional certificate extension and the server_name extension Record Headers Certificate … Cert Headers Cert Signature Algorithm Issuer Validity Period Subject Subject Public Key Optional Info Cert Sig Alg Cert Signature BRKSEC-2809 25
- 26. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public TLS Client Fingerprinting Record Headers ClientHello Random Nonce [Session ID] Cipher suites Compression Methods Extensions Used for fingerprinting 0.9.8 1.0.0 1.0.1 1.0.2 OpenSSL Versions BRKSEC-2809 26
- 27. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Classification Model on SPLT and BD Length transition bins Time transition bins Classifier Feature Selection [0,1] BRKSEC-2809 28
- 28. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Evaluating Algorithms BRKSEC-2809 29
- 29. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • Malware • August 2015 to May 2016 pcaps from ThreatGRID • TLS (443) traffic, > 100 in and out bytes • 225,740 flows, Telemetry enhanced with TLS extensions, ciphersuites, and public key lengths • Benign • traffic taken from a large enterprise DMZ • TLS (443) traffic, > 100 in and out bytes • 225,000 flows, Telemetry enhanced with TLS extensions, ciphersuites, and public key lengths • 10-fold cross-validation Test Setup BRKSEC-2809 30
- 30. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public src dst • Packet Lengths and Inter-arrival Times Modeled as 1st Order Markov Chains • Probabilities of Byte Values in Payload • Binary Vector of Offered Ciphersuites and Extensions, and Client’s Public Key Size Intraflow Features BRKSEC-2809 31
- 31. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Results • L1-logistic regression • Meta + SPLT + BD • 0.01% FDR: 1.3% • Total Accuracy: 98.9% • L1-logistic regression • Meta + SPLT + BD + TLS • 0.01% FDR: 92.8% • Total Accuracy: 99.6% BRKSEC-2809 32
- 32. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Results (without Schannel) • L1-logistic regression • Meta + SPLT + BD • 0.01 FDR: 0.9% • Total Accuracy: 98.5% • L1-logistic regression • Meta + SPLT + BD + TLS • 0.01 FDR: 87.2% • Total Accuracy: 99.6% BRKSEC-2809 33
- 33. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Per-Family Classification Results Malware Family Meta+SPLT+BD Meta+SPLT+BD+TLS Bergat* 100.0% 100.0% Sality* 95.0% 97.7% Dridex 16.5% 78.5% Skeeyah 95.9% 98.6% Virlock 100.0% 100.0% BRKSEC-2809 34
- 34. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • Malware • August 2015 to May 2016 pcaps from ThreatGRID • TLS (443) traffic, > 100 in and out bytes • 13,542 flows with all available data (~63.2% of malicious TLS flows) • Benign • traffic taken from a large enterprise DMZ • TLS (443) traffic, > 100 in and out bytes • 42,927 flows with all available data (~3.8% of benign TLS flows) • 10-fold cross-validation Test Setup BRKSEC-2809 35
- 35. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public src dst • Packet Lengths and Inter-arrival Times Modeled as 1st Order Markov Chains • Probabilities of Byte Values in Payload • Binary Vector of Offered Ciphersuites and Extensions, and Client’s Public Key Size Intraflow Features BRKSEC-2809 36
- 36. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • DNS • Alexa Lists • Lengths of DN and FQDN • Suffix • TTL • % Numerical Characters • % Non-alphanumeric Chars • HTTP • Outbound/inbound header fields • Content-Type • User-Agent • Accept-Language • Server • code Contextual Flow Features BRKSEC-2809 37
- 37. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • L1-logistic regression • Traditional Side Channel Features • 0.00% FDR: 0.00% • Total Accuracy: 93.1% • L1-logistic regression • All Available Features • 0.00% FDR: 99.9% • Total Accuracy: 99.9% Results (10-fold cross-validation) BRKSEC-2809 38
- 38. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Detecting Encrypted Malware Acc. 0.00% FDR SPLT+BD+TLS+HTTP+DNS 99.993% 99.978% TLS 94.836% 50.406% DNS 99.496% 94.654% HTTP 99.945% 98.996% TLS+DNS 99.883% 96.551% TLS+HTTP 99.955% 99.660% HTTP+DNS 99.985% 99.956% SPLT+BD+TLS 99.933% 70.351% SPLT+BD+TLS+DNS 99.968% 98.043% SPLT+BD+TLS+HTTP 99.983% 99.956% TLS DNS HTTP SPLT+BD BRKSEC-2809 39
- 39. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Interpretability • Malware Features • DNS Suffix: org • DNS TTL: 3600 • TLS_RSA_WITH_RC4_128_SHA • HTTP Field: location • DNS Alexa: Not Found • HTTP Server: nginx • HTTP Code: 404 • Benign Features • TLS Ext: extended_master_secret • Content type: application/octet-stream • TLS_DHE_RSA_WITH_DES_CBC_SHA • HTTP Server: Microsoft-IIS/8.5 • DNS Alexa: top-1,000,000 • HTTP User-Agent: Microsoft-CryptoAPI/6.1 BRKSEC-2809 40
- 40. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public • Datasets are relatively limited • Evasion is possible • Not impossible to mimic popular TLS/HTTP/DNS clients/servers/responses • But, mimicking these features requires an on-going and non-trivial software engineering effort • Can (hopefully) limit evasion attacks • Identify most robust network features (several good existing algorithms) • Include higher order interactions: • TLS client / HTTP user agent(s) • Ordering of offered ciphersuites and HTTP fields Caveats / Biases BRKSEC-2809 41
- 41. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public Conclusions • Malware’s use of TLS is increasing • Our research complements current solutions • Machine learning/rules applied to passively obtained network data features can detect malware communication • https://github.com/cisco/joy • Note: contact authors to obtain well-trained classifier parameters 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% Percentage of malware traffic using TLS BRKSEC-2809 42
- 42. © 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public https://arxiv.org/abs/1607.01639 Название: «Deciphering Malware's use of TLS (without Decryption)» Авторы: Blake Anderson, Subharthi Paul, David McGrew Препринт статьи, на основе которой сделана данная презентация, доступен по адресу: 43
- 43. Q & A
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