Multiple vulnerabilities in yaSSL 1.7.5

[Luigi Auriemma <aluigi@xxxxxxxxxxxxx>]

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                             Luigi Auriemma

Application:  yaSSL
              http://www.yassl.com
Versions:     <= 1.7.5
Platforms:    Windows and *nix
Bugs:         A] buffer-overflow in ProcessOldClientHello
              B] buffer-overflow in "input_buffer& operator>>"
              C] invalid memory access in HASHwithTransform::Update
Exploitation: remote
Date:         04 Jan 2008
Author:       Luigi Auriemma
              e-mail: aluigi@xxxxxxxxxxxxx
              web:    aluigi.org


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1) Introduction
2) Bugs
3) The Code
4) Fix


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===============
1) Introduction
===============


yaSSL is an open source SSL library mainly used in MySQL and in other
projects.
On MySQL, if SSL support is enabled, is possible to use this
vulnerability for pre-authentication code execution.


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=======
2) Bugs
=======

-------------------------------------------
A] buffer-overflow in ProcessOldClientHello
-------------------------------------------

The buffer which contains the data received by the client in the Hello
packet has the following structure (from yassl_imp.hpp):

class ClientHello : public HandShakeBase {
    ProtocolVersion     client_version_;
    Random              random_;
    uint8               id_len_;                         // session id length
    opaque              session_id_[ID_LEN];
    uint16              suite_len_;                      // cipher suite length
    opaque              cipher_suites_[MAX_SUITE_SZ];
    uint8               comp_len_;                       // compression length
    CompressionMethod   compression_methods_;
    ...

where ID_LEN is 32 elements long, MAX_SUITE_SZ 64 and RAN_LEN (Random)
is 32.
The ProcessOldClientHello function called when an old version of the
Hello packet is received doesn't have the needed checks for limiting
the amount of data which will fill these 3 fields leading to a
buffer-overflow vulnerability exploitable for executing code remotely.

>From handshake.cpp:

void ProcessOldClientHello(input_buffer& input, SSL& ssl)
    ...
    ClientHello ch;
    ...
    for (uint16 i = 0; i < ch.suite_len_; i += 3) {    
        byte first = input[AUTO];
        if (first)  // sslv2 type
            input.read(len, SUITE_LEN); // skip
        else {
            input.read(&ch.cipher_suites_[j], SUITE_LEN);
            j += SUITE_LEN;
        }
    }
    ch.suite_len_ = j;

    if (ch.id_len_)
        input.read(ch.session_id_, ch.id_len_);

    if (randomLen < RAN_LEN)
        memset(ch.random_, 0, RAN_LEN - randomLen);
    input.read(&ch.random_[RAN_LEN - randomLen], randomLen);
    ...


------------------------------------------------
B] buffer-overflow in "input_buffer& operator>>"
------------------------------------------------

Another buffer-overflow is located in the function used for handling
the normal Hello packet but in this case doesn't seem possible (or
easily possible) to exploit this vulnerability for executing code.

>From yassl_imp.cpp:

input_buffer& operator>>(input_buffer& input, ClientHello& hello)
    ...
    hello.id_len_ = input[AUTO];
    if (hello.id_len_) input.read(hello.session_id_, ID_LEN);
    
    // Suites
    byte tmp[2];
    tmp[0] = input[AUTO];
    tmp[1] = input[AUTO];
    ato16(tmp, hello.suite_len_);
    input.read(hello.cipher_suites_, hello.suite_len_);
    ...


-----------------------------------------------------
C] invalid memory access in HASHwithTransform::Update
-----------------------------------------------------

The usage of a too big size value in the Hello packet leads to a crash
of the library through the reading of data outside the memory
containing the incoming packet.

>From hash.cpp:

void HASHwithTransform::Update(const byte* data, word32 len)
{
    // do block size increments
    word32 blockSz = getBlockSize();
    byte*  local   = reinterpret_cast<byte*>(buffer_);

    while (len) {
        word32 add = min(len, blockSz - buffLen_);
        memcpy(&local[buffLen_], data, add);
        ...


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===========
3) The Code
===========


http://aluigi.org/poc/yasslick.zip


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======
4) Fix
======


A mail has been sent to the developers yesterday during my tests only
to inform them of the vulnerabilities.


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--- 
Luigi Auriemma
http://aluigi.org