Network – Offensive Security (N.O.S), Part 1: CAM Table Overflow

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Lets straight to the point, I’ll break down this article into 4 sub-chapter:

  • The Theory
  • The Attack and The Outcome
  • The Mitigation

Security Experts says: “Security is as good as layer belows” or “Security is as strong as weakest link

Dalam 7 OSI Layer…klo dari bawahnya aja udah kena (physical and data link)…keatas2nya juga akan kena (domino effect)

Wokeh, lets prepare the ingredients:

  • Manageable Switch (klo pake switch biasa ga keliatan apa yang mau dipraktekin)
  • Kali Linux (for me its 2016 version)
  • Another PC (I use Kali and Windows in same host a.k.a Virtual Machine)


The Theory

Setiap switch pasti punya yang namanya CAM Table

For you who doesn’t know what CAM table mean, take a look at this pic below

Yup…mac address table

CAM table ini berguna bagi switch untuk switching traffic *yea right man -_-; …

Lah, bener kan…switch itu bahasa indonesianya apa? pengalihan/menukar (if you recall how switch works then you’ll understand that switch is replacing mac-address for each hop both source and destination address)

هي문제는 (wkwkwk…all same meaning: the problem is)

Setiap switch naro CAM table ini di ASIC chip

And…because of hardware characteristics…there is….a limitation


The answer may vary, switch cisco cat6800 can store 128k mac addresses while cat 2960 only hold maybe 8000 mac addresses

So, what happens when the table goes full? OVERFLOW OF BROADCAST…switch revert to hub (being able to broadcast traffic only), this is the fallback mechanism of switch if its table is full

Anddd that is the goals…broadcast the traffic so we can see what being send and receive, or even worse…bring down the network


Attack and Outcome

Gw pake cisco cat3750…show mac address-table count menunjukkan bahwa ini switch sanggup nampung sekitar 6000an mac addresses

And start that kali linux…open terminal, just type macof (mac address overflow)

Anddd….now this kali linux will flood the switch with a ton of bogus mac addresses

In a matter of second (ga sampe 5 detik malah), lets see the CAM table again

From the previous 6003 down to 40…that how you bring down the network…

Makanya gw bilang jgn pake switch biasa, ga ketauan mac address table nya abis apa engga/diserang apa kaga nya

Impactnya…?? Ga usa jauh2 untuk bring down network, lets bring another brother of kali, the red hat

Gw pake RHEL 7, ip-nya

Trus gw ping ke (gateway)…dan di kali linux gw jalanin wireshark…apply filter ip.addr ==

Now we see the traffic come back and forth…ini baru ping, bagaimana klo dia ngirim sensitive data? Dengan adanya broadcast…attacker can sniff through wireshark


The Mitigation

  1. Port Security (link)
  2. An even better solution: shutdown all unused port

That’s it guys…next lets try another network-offensive security attack (if I have time to do that 😉 )

This is going to be my next writing article…network security attack…(N.O.S), do you like it? Leave a comment…

Configuring FlexVPN Site-to-Site with Digital Certificate

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See here (see chapter “Authentication”) if you don’t know about Digital Certificate (a.k.a PKI a.k.a public key infrastructure a.k.a CA a.k.a Certificate Authority)

Now the question is…what is FlexVPN?

FlexVPN is Cisco terminology of VPN that can be connected and authenticate via multiple terms (in this case I’ll show you the Digital Certificate ways, VPN biasa juga bisa sih)

FlexVPN Benefits:

  • Bisa di deploy di MPLS Network (private or public)
  • Can accept both site-to-site and remote VPN at the same time
  • Failover Redudancy (can be done via dynamic routing over FlexVPN interface tunnel)
  • 3rd party compatibility…this is it…ga harus VPN ama cisco devices juga hahaha
  • Multicast support
  • Advanced QoS (bisa ditaro langsung pas traffic mau jalan atau di hub router-nya aja)
  • VRF awareness, cocok buat ISP

Mudah2an klo sempet kita oprek satu2 ini benefit2nya…bener kaga yang Cisco bilang…

Warning: FlexVPN relies heavily on the powerful IKEv2 (see here) to get it working, that why this VPN is so “flexible”…so, get you’re a** down to the new successor of ISAKMP and IKEv1…

Note: IOS 7200 15.4 ga lengkap config PKI server-nya, gw pake 3640 yang lama (surprisingly complete configuration about PKI server…)

DAN GUA BARU TAU TERNYATA ROUTER CISCO BISA JADI PKI SERVER!!! Gua kira harus pake VMware isi Windows Server….


The Idea and Network Design

Jadi HQ-R1 akan konek dengan BR-R2 via VPN…awalnya pake pre-shared-key (PSK), nanti kita ganti pake digital certificate (minta dari R3)


Configure IKEv2 first on both Routers

On HQ-R1 (and BR-R2 with necessary changes)

First…the hostname and domain (kepake nanti buat Digital Certificate, wajib ada hostname sama domain soalnya)

Second…Configure IKEv2 Keyring

Awalnya kita pake pre-shared-key untuk konek vpn (passwordnya “PSK”)

Third…Configure IKEv2 Profile


IKEv2 bisa asymmetric authentication (dia/local pake PSK, klo remote pake yang lain…kasus diatas sama2 pake PSK)

DPD (dead peer detection)…fitur yang include secara default di IKEv2 framework untuk ngedeteksi peer/ujung yang satu VPN-nya mati, 60..intervalnya, 2…nyoba 2x, on-demand…ya klo lagi butuh (ada settingan periodic kok)

Fourth…Configure IPsec profile with IKEv2 profile we created before

Fifth…Configure interface tunnel for private traffic and attach that ipsec profile in, don’t forget that ip route too

Verification…ping from loopback R1 (100.1) to R2 loopback (200.1) and type “show crypto ikev2 session” untuk liat ada IKEv2 proses ga pas lagi ping-pingan

show crypto ikev2 session


Configure certificate on R3-CA-SRV

Now….im actually amazed by Cisco Router to act like CA Server…lets see the configuration

Untuk jadi CA ada beberapa hal yang harus diperhatikan

  • Ganti hostname
  • Harus ada domain-name
  • Harus di set NTP (atau minimal clock-nya dibenerin)
  • Enable http…soalnya request certificate-nya dari port 80 (klo lo pernah setting2 PKI/CA di windows…pasti lu ngerti)
  • Settingan CA-nya…with crypto pki server [nama SERVER] seperti dibawah ini:

crypto pki server

Kasi password (contoh: cisco123), jadi klo ada yang mau minta request dibikin sertifikat (kek kita minta KTP ke kelurahan, istilahnya: ENROLL) harus tau password-nya

Jangan lupa di “no shutdown” untuk aktifin CA-nya


HQ-R1 enrollment to CA-SRV and change the authentication method from PSK to Digital Certificate

Ceritanya HQ-R1 minta dibikinin sertifikat ama R3-CA-SRV, soalnya dia mau konek VPN-an ama BR-R2, biar ga pake PSK (jablay?!?) lagi…

Klo pake PSK kan masalahnya pasti itu2 aja…kebanyakan PSK…kena raja singa…

Maksudnya…klo mau ke R2 pake kunci A, klo mau ke R3 pake kunci B, klo mau ke R4,R5,R6,R7..dll??…gantungan kunci kita bawa (not preferable with Company with many branch)

First…bikin dulu path ke R3-CA-SRV buat request certificate

Look at keyword enrollment…pake URL ke port 80 (that’s what I mean enable http in R3-CA-SRV)

Trus ketik “crypto pki authenticate [nama CA]“…klo berhasil nanti R3 akan ngasi certificate dengan fingerprint unique punya dia

perhatiin Fingerprintnya…sama ga (nanti pas di BR-R2 kita bandingin)

Second, enroll…minta bikinin sertifikat dongss pake “crypto pki enroll [nama CA]”

crypto pki enroll

Nanti ada beberapa pertanyaan…intinya pas “request certificate from CA“…ketik “yes

Now…lets change HQ-R1 authentication method to RSA-SIG (digital certificate) from trustpoint CA kita and with identity pake dn (distinguished name…itu tu…HQ-R1.cisco.com)

And then…Verification


Change authentication behavior BR-R2 using Certificate if HQ-R1 wants to connect

Pretty much the same…tentuin CA path-nya

See…FINGERPRINT-nya sama kan kek HQ-R1…(check sendiri konfigurasi R1 diatas)

Trus…bikin certificate map…biar klo ada mau konek ke BR-R2, pake metode yang ada certificate map itu…trus masukin deh itu map ke IKEv2 profile-nya

kita bisa liat diatas…klo ada yg mau konek ke BR-R2, tolong tunjukin certificate-nya, dan dia hanya percaya sama certificate yang dari CA-SRV yang kita tunjuk tadi



Shut and then no shut int tunnel-nya, biar refresh ulang IKEv2 negosiasinya

show crypto ikev2 sa de

Di HQ-R1…dia mau VPN ke BR-R2 pake RSA…

Dan di BR_R2 (gambar dibawah)…klo ada yang mau konek pake verifikasi RSA…

show crypto ikev2 sa de 2

And…im done






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