Sunday, October 08, 2006

Security through Obscurity - I (Login banner)

"Obscurity is not security, but... obscurity is a layer of security!" - Монголоор харин "өнгөлөн далдлалт бол нууцлал хамгаалал биш, гэхдээ түүний нэг хэсэг юм" гэчихвэл хэлэх гэсэн санаа нь гараад байна. Юу вэ гэхээр, ач холбогдолгүй гэмээр жижигхэн зүйлс ч нууцлал хамгааллыг хангахад чухал шүү гэсэн санаа...

Энэ удаад та бүхэнд "login banner"-г танилцуулж байна.

Гадны хүн нэвтрэх хориотой газруудад "гадны хүн орохыг хориглоно!", "staff only!" гэсэн бичгүүдийг та бүхэн зөндөө л харсан байх. Энэ нь тухайн газрын дотоод ба гадаад хил хязгаарыг зааглан тогтоож өгч байгаагаас гадна энэ хил хязгаарыг зөвшөөрөлгүй давсан хүнд хариуцлага ноогдуулна гэдгийг маш товчхоноор хэлж өгч байгаа билээ. Хэрвээ ийм бичиг байхгүй байсан бол яах вэ? ... Мэдээж будилж яваа хүмүүс ч юмуу, эсвэл дэмий сониуч хүмүүс орох ёсгүй газарлуу ороод л явчихна гэсэн үг. Тэгхээр "login banner"-г системрүү нэвтэрч байгаа хил хязгаар бүрт тавьж өгөх нь ямар ач холбогдолтой болохыг та бүхэн ойлгосон байх.

Login banner гэхээр дүрэм журам, бүхэл бүтэн нүүр дүүрэн зүйл байх хэрэггүй. Гүйлгээд уншихад, гол нь "unauthorized use is prohibited...", "activities are reported..." гэсэн үгнүүд байхаар бичигдсэн байх хэрэгтэй. Энэ нь "зөвшөөрөлгүй системд нэвтрэхийг хориглоно,хийсэн зүйлүүдийг чинь хуулийн байгууллагад шилжүүлэх эрхтэй" гэсэн санааг агуулж байгаа юм. Би систем дээрээ жишээлбэл:

******************************************************
Authorized uses only!!!
All access to this system is monitored and reported!!!
******************************************************


гэсэн баннер тавьсан. Системрүүгээ орох болгондоо, энэ үгийг уншдаг. Тэгээд жижигхэн ч гэсэн хариуцлага мэдэрч, урдынхаасаа илүү нямбай ажиллах болсон. Харин гадны хэн нэгний хувьд ийм үгстэй тулгарвал хэсэгхэн зуур ч гэсэн тээнэгэлзэж эргэлзэх нь мэдээж...

Харин би анх энэ санаагаа MUG-н нийтэд зориулсан shell server-н login banner-с авсан. Энэ баннерийг бүгдээрээ одоо харцгаая:


#################################################
# Sign up for a free shell account from ...
# MICOM CO., LTD
#################################################


do not misuse the server for hacking purpose!
Credit to HBX and hairball :)

HBX ба hairball гэж хэн болохыг g0mb0 ах маань хэлж өгөх байх :). Харин энэ сервер дээр ажиллахдаа бусдын эрх ашгийг хүндэтгэхийг энэхүү баннер хэлж өгч байна даа...


login banner хэрхэн тавих вэ?

1. SSH-н хувьд sshd_config файл дотор

Banner /etc/ssh/ssh_banner

мөрийг нэмснээр "/etc/ssh/ssh_banner" гэсэн текст файл доторхийг хэрэглэгч login хийж орохын өмнө дэлгэцэн дээр хэвлэнэ... гэхдээ login prompt дээр username-г бичсэний дараа хэвлэнэ.

2. Unix төрлийн үйлдлийн системд хэрэглэгч логин хийж орсны дараах login banner-г тавиж болно. Үүний тулд "/etc/motd" файл доторхыг өөрчилнө, хэрэв ийм файл байхгүй бол үүсгэж өгнө. Мэдээж хэрэглэгч системд нэвтэрсний дараа гарах баннер учир "орохыг хориглоно" гэсэн үгс байхгүй нь мэдээж. Энд ихэвчлэн хэрэглэгчдэд хандсан сануулга, эсвэл компаний лого, системийн цаг... гэх мэтчилэн юу дуртайгаа оруулж болно.


Obscurity is not security, but... obscurity is a layer of security!

34 comments:

Erkhemee said...

bi budilj yavj bgaad bayanaa-giin server ruu root erheer orchihvol yanaa :)) Nargia bailaa..
dajgui niitlel bn.

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