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by lostmsu 1985 days ago
That only works if the string is the same each time. But it won't, if it changes like TOTP code.
2 comments
k1t 1985 days ago
If all you are comparing is HASH(random_string + hashed_password) then it will still work.

The server will give me random_string and I know hashed_password from the DB leak.

Obviously this assumes the login process actually works as described in the earlier post.

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lostmsu 1984 days ago
That protects hashes from leaking in transit, for the scenario with 3rd party TLS terminators mentioned above.
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jarkhen 1985 days ago
If the string changes each time, how could they possibly have the matching hashed password stored in the database?
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fgonzag 1985 days ago
They have the users password hash stored in their db so they can replicate the process server side:

login_token = hash(pwd_hash + nonce)

its nothing too wild, especially considering the age of yahoo mail.

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jarkhen 1985 days ago
Ah, right, I misread the original description of what they were doing.

As is, then, it really is just making the hashed password the new password. If I can get the hashed password out of the DB, I can load the login page and simply skip the initial hashing step that's done on the frontend. I now have access to the account without ever knowing the original password.

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SAI_Peregrinus 1984 days ago
Except that it's easy (indeed, required for security) to change the nonce for each login request, so you can't just replay the hash.
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jarkhen 1984 days ago
That protects against an attacker reading network traffic. It does not protect against an attacker that has the hashed password from the DB.

The only thing you need in order to authenticate at any given time is the hash of (hashed password + nonce). The latter you get for free, at any time, from the server, so you only need to know the hashed password -- not the password itself. Since the hashed password is directly stored in the DB, if you get your hands on that you can authenticate.

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SAI_Peregrinus 1984 days ago
Right. My mistake. I should have thought it through more thoroughly before posting. Hopefully my comment doesn't mislead anyone, I'll try to do better in the future.
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