static int ssl_parse_client_hello_v2( mbedtls_ssl_context *ssl )
{
    int ret, got_common_suite;
    unsigned int i, j;
    size_t n;
    unsigned int ciph_len, sess_len, chal_len;
    unsigned char *buf, *p;
    const int *ciphersuites;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse client hello v2" ) );

#if defined(MBEDTLS_SSL_RENEGOTIATION)
    if( ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "client hello v2 illegal for renegotiation" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }
#endif /* MBEDTLS_SSL_RENEGOTIATION */

    buf = ssl->in_hdr;

    MBEDTLS_SSL_DEBUG_BUF( 4, "record header", buf, 5 );

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v2, message type: %d",
                   buf[2] ) );
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v2, message len.: %d",
                   ( ( buf[0] & 0x7F ) << 8 ) | buf[1] ) );
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v2, max. version: [%d:%d]",
                   buf[3], buf[4] ) );

    /*
     * SSLv2 Client Hello
     *
     * Record layer:
     *     0  .   1   message length
     *
     * SSL layer:
     *     2  .   2   message type
     *     3  .   4   protocol version
     */
    if( buf[2] != MBEDTLS_SSL_HS_CLIENT_HELLO ||
        buf[3] != MBEDTLS_SSL_MAJOR_VERSION_3 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }

    n = ( ( buf[0] << 8 ) | buf[1] ) & 0x7FFF;

    if( n < 17 || n > 512 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }

    ssl->major_ver = MBEDTLS_SSL_MAJOR_VERSION_3;
    ssl->minor_ver = ( buf[4] <= ssl->conf->max_minor_ver )
                     ? buf[4]  : ssl->conf->max_minor_ver;

    if( ssl->minor_ver < ssl->conf->min_minor_ver )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "client only supports ssl smaller than minimum"
                            " [%d:%d] < [%d:%d]",
                            ssl->major_ver, ssl->minor_ver,
                            ssl->conf->min_major_ver, ssl->conf->min_minor_ver ) );

        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                     MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION );
        return( MBEDTLS_ERR_SSL_BAD_HS_PROTOCOL_VERSION );
    }

    ssl->handshake->max_major_ver = buf[3];
    ssl->handshake->max_minor_ver = buf[4];

    if( ( ret = mbedtls_ssl_fetch_input( ssl, 2 + n ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_fetch_input", ret );
        return( ret );
    }

    ssl->handshake->update_checksum( ssl, buf + 2, n );

    buf = ssl->in_msg;
    n = ssl->in_left - 5;

    /*
     *    0  .   1   ciphersuitelist length
     *    2  .   3   session id length
     *    4  .   5   challenge length
     *    6  .  ..   ciphersuitelist
     *   ..  .  ..   session id
     *   ..  .  ..   challenge
     */
    MBEDTLS_SSL_DEBUG_BUF( 4, "record contents", buf, n );

    ciph_len = ( buf[0] << 8 ) | buf[1];
    sess_len = ( buf[2] << 8 ) | buf[3];
    chal_len = ( buf[4] << 8 ) | buf[5];

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciph_len: %d, sess_len: %d, chal_len: %d",
                   ciph_len, sess_len, chal_len ) );

    /*
     * Make sure each parameter length is valid
     */
    if( ciph_len < 3 || ( ciph_len % 3 ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }

    if( sess_len > 32 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }

    if( chal_len < 8 || chal_len > 32 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }

    if( n != 6 + ciph_len + sess_len + chal_len )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }

    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, ciphersuitelist",
                   buf + 6, ciph_len );
    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, session id",
                   buf + 6 + ciph_len, sess_len );
    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, challenge",
                   buf + 6 + ciph_len + sess_len, chal_len );

    p = buf + 6 + ciph_len;
    ssl->session_negotiate->id_len = sess_len;
    memset( ssl->session_negotiate->id, 0,
            sizeof( ssl->session_negotiate->id ) );
    memcpy( ssl->session_negotiate->id, p, ssl->session_negotiate->id_len );

    p += sess_len;
    memset( ssl->handshake->randbytes, 0, 64 );
    memcpy( ssl->handshake->randbytes + 32 - chal_len, p, chal_len );

    /*
     * Check for TLS_EMPTY_RENEGOTIATION_INFO_SCSV
     */
    for( i = 0, p = buf + 6; i < ciph_len; i += 3, p += 3 )
    {
        if( p[0] == 0 && p[1] == 0 && p[2] == MBEDTLS_SSL_EMPTY_RENEGOTIATION_INFO )
        {
            MBEDTLS_SSL_DEBUG_MSG( 3, ( "received TLS_EMPTY_RENEGOTIATION_INFO " ) );
#if defined(MBEDTLS_SSL_RENEGOTIATION)
            if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "received RENEGOTIATION SCSV "
                                    "during renegotiation" ) );

                mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
                return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
            }
#endif /* MBEDTLS_SSL_RENEGOTIATION */
            ssl->secure_renegotiation = MBEDTLS_SSL_SECURE_RENEGOTIATION;
            break;
        }
    }

#if defined(MBEDTLS_SSL_FALLBACK_SCSV)
    for( i = 0, p = buf + 6; i < ciph_len; i += 3, p += 3 )
    {
        if( p[0] == 0 &&
            p[1] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE >> 8 ) & 0xff ) &&
            p[2] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE      ) & 0xff ) )
        {
            MBEDTLS_SSL_DEBUG_MSG( 3, ( "received FALLBACK_SCSV" ) );

            if( ssl->minor_ver < ssl->conf->max_minor_ver )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "inapropriate fallback" ) );

                mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INAPROPRIATE_FALLBACK );

                return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
            }

            break;
        }
    }
#endif /* MBEDTLS_SSL_FALLBACK_SCSV */

    got_common_suite = 0;
    ciphersuites = ssl->conf->ciphersuite_list[ssl->minor_ver];
    ciphersuite_info = NULL;
#if defined(MBEDTLS_SSL_SRV_RESPECT_CLIENT_PREFERENCE)
    for( j = 0, p = buf + 6; j < ciph_len; j += 3, p += 3 )
        for( i = 0; ciphersuites[i] != 0; i++ )
#else
    for( i = 0; ciphersuites[i] != 0; i++ )
        for( j = 0, p = buf + 6; j < ciph_len; j += 3, p += 3 )
#endif
        {
            if( p[0] != 0 ||
                p[1] != ( ( ciphersuites[i] >> 8 ) & 0xFF ) ||
                p[2] != ( ( ciphersuites[i]      ) & 0xFF ) )
                continue;

            got_common_suite = 1;

            if( ( ret = ssl_ciphersuite_match( ssl, ciphersuites[i],
                                               &ciphersuite_info ) ) != 0 )
                return( ret );

            if( ciphersuite_info != NULL )
                goto have_ciphersuite_v2;
        }

    if( got_common_suite )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got ciphersuites in common, "
                            "but none of them usable" ) );
        return( MBEDTLS_ERR_SSL_NO_USABLE_CIPHERSUITE );
    }
    else
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no ciphersuites in common" ) );
        return( MBEDTLS_ERR_SSL_NO_CIPHER_CHOSEN );
    }

have_ciphersuite_v2:
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "selected ciphersuite: %s", ciphersuite_info->name ) );

    ssl->session_negotiate->ciphersuite = ciphersuites[i];
    ssl->transform_negotiate->ciphersuite_info = ciphersuite_info;

    /*
     * SSLv2 Client Hello relevant renegotiation security checks
     */
    if( ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
        ssl->conf->allow_legacy_renegotiation == MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "legacy renegotiation, breaking off handshake" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
    }

    ssl->in_left = 0;
    ssl->state++;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse client hello v2" ) );

    return( 0 );
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.